This document is free software; you can redistribute and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

This document is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.

This manual describes how to use and administer CVS (Concurrent Versions
System). It is part of a larger work entitled Open Source
Development With CVS; please see the introduction for details.

Introduction

This is a set of free, online chapters about using CVS (Concurrent
Versions System) for collaboration and version control. It covers
everything from CVS installation and basic concepts all the way to
advanced usage and administration. It is intended for anyone who uses
or plans to use CVS.

These chapters are excerpted from a larger work called Open Source
Development With CVS (published by The Coriolis Group, ISBN 1-57610-490-7). The remainder of that book -
chapters 1, 3, 5, and 7 - deals with the challenges and philosophical
issues of running an Open Source project using CVS.

An Overview of CVS

I can't imagine programming without it... that would be like
parachuting without a parachute!

-Brian Fitzpatrick on CVS

This chapter introduces the fundamentals of CVS, and then provides an
in-depth guided tour of everyday CVS usage. Concepts are presented
sequentially, so if you're new to CVS, the best way to read this is to
start at the beginning and go straight through, without skipping
anything.

Basic Concepts

If you've never used CVS (or any version control system) before, it's
easy to get tripped up by some of its underlying assumptions. What
seems to cause the most initial confusion about CVS is that it is used
for two apparently unrelated purposes: record keeping and collaboration.
It turns out, however, that these two functions are closely connected.

Record keeping became necessary because people wanted to compare a
program's current state with how it was at some point in the past. For
example, in the normal course of implementing a new feature, a developer
may bring the program into a thoroughly broken state, where it will
probably remain until the feature is mostly finished. Unfortunately,
this is just the time when someone usually calls to report a bug in the
last publicly released version. To debug the problem (which may also
exist in the current version of the sources), the program has to be
brought back to a useable state.

Restoring the state poses no difficulty if the source code history is
kept under CVS. The developer can simply say, in effect, "Give me the
program as it was three weeks ago", or perhaps "Give me the program as
it was at the time of our last public release". If you've never had
this kind of convenient access to historical snapshots before, you may
be surprised at how quickly you come to depend on it. Personally, I
always use revision control on my coding projects now - it's saved me
many times.

To understand what this has to do with facilitating collaboration, we'll
need to take a closer look at the mechanism that CVS provides to help
numerous people work on the same project. But before we do that, let's
take a look at a mechanism that CVS doesn't provide (or at least,
doesn't encourage): file locking. If you've used other version control
systems, you may be familiar with the lock-modify-unlock development
model, wherein a developer first obtains exclusive write access (a lock)
to the file to be edited, makes the changes, and then releases the lock
to allow other developers access to the file. If someone else already
has a lock on the file, they have to "release" it before you can lock it
and start making changes (or, in some implementations, you may "steal"
their lock, but that is often an unpleasant surprise for them and not
good practice!).

This system is workable if the developers know each other, know who's
planning to do what at any given time, and can communicate with each
other quickly if someone cannot work because of access contention.
However, if the developer group becomes too large or too spread out,
dealing with all the locking issues begins to chip away at coding time;
it becomes a constant hassle that can discourage people from getting
real work done.

CVS takes a more mellow approach. Rather than requiring that developers
coordinate with each other to avoid conflicts, CVS enables developers to
edit simultaneously, assumes the burden of integrating all the changes,
and keeps track of any conflicts. This process uses the
copy-modify-merge model, which works as follows:

Developer A requests a working copy (a directory tree containing the
files that make up the project) from CVS. This is also known as
"checking out" a working copy, like checking a book out of the library.

Developer A edits freely in her working copy. At the same time, other
developers may be busy in their own working copies. Because these are
all separate copies, there is no interference - it is as though all of
the developers have their own copy of the same library book, and they're
all at work scribbling comments in the margins or rewriting certain
pages independently.

Developer A finishes her changes and commits them into CVS along with a
"log message", which is a comment explaining the nature and purpose of
the changes. This is like informing the library of what changes she
made to the book and why. The library then incorporates these changes
into a "master" copy, where they are recorded for all time.

Meanwhile, other developers can have CVS query the library to see if the
master copy has changed recently. If it has, CVS automatically updates
their working copies. (This part is magical and wonderful, and I hope
you appreciate it. Imagine how different the world would be if real
books worked this way!)

As far as CVS is concerned, all developers on a project are equal.
Deciding when to update or when to commit is largely a matter of
personal preference or project policy. One common strategy for coding
projects is to always update before commencing work on a major change
and to commit only when the changes are complete and tested so that the
master copy is always in a "runnable" state.

Perhaps you're wondering what happens when developers A and B, each in
their own working copy, make different changes to the same area of text
and then both commit their changes? This is called a conflict, and
CVS notices it as soon as developer B tries to commit changes. Instead
of allowing developer B to proceed, CVS announces that it has discovered
a conflict and places conflict markers (easily recognizable textual
flags) at the conflicting location in his copy. That location also
shows both sets of changes, arranged for easy comparison. Developer B
must sort it all out and commit a new revision with the conflict
resolved. Perhaps the two developers will need to talk to each other to
settle the issue. CVS only alerts the developers that there is a
conflict; it's up to human beings to actually resolve it.

What about the master copy? In official CVS terminology, it is called
the project's repository. The repository is simply a file tree kept on
a central server. Without going into too much detail about its
structure (but see Repository Administration), let's look at what
the repository must do to meet the requirements of the
checkout-commit-update cycle. Consider the following scenario:

Two developers, A and B, check out working copies of a project at the
same time. The project is at its starting point - no changes have been
committed by anyone yet, so all the files are in their original,
pristine state.

Developer A gets right to work and soon commits her first batch of
changes.

Meanwhile, developer B watches television.

Developer A, hacking away like there's no tomorrow, commits her second
batch of changes. Now, the repository's history contains the original
files, followed by A's first batch of changes, followed by this set of
changes.

Meanwhile, developer B plays video games.

Suddenly, developer C joins the project and checks out a working copy
from the repository. Developer C's copy reflects A's first two sets of
changes, because they were already in the repository when C checked out
her copy.

Developer A, continuing to code as one possessed by spirits, completes
and commits her third batch of changes.

Finally, blissfully unaware of the recent frenzy of activity, developer
B decides it's time to start work. He doesn't bother to update his
copy; he just commences editing files, some of which may be files that A
has worked in. Shortly thereafter, developer B commits his first
changes.

At this point, one of two things can happen. If none of the files
edited by developer B have been edited by A, the commit succeeds.
However, if CVS realizes that some of B's files are out of date with
respect to the repository's latest copies, and those files have also
been changed by B in his working copy, CVS informs B that he must do an
update before committing those files.

When developer B runs the update, CVS merges all of A's changes into B's
local copies of the files. Some of A's work may conflict with B's
uncommitted changes, and some may not. Those parts that don't are
simply applied to B's copies without further complication, but the
conflicting changes must be resolved by B before being committed.

If developer C does an update now, she'll receive various new changes
from the repository: those from A's third commit, and those from B's
first successful commit (which might really come from B's second
attempt to commit, assuming B's first attempt resulted in B being forced
to resolve conflicts).

In order for CVS to serve up changes, in the correct sequence, to
developers whose working copies may be out of sync by varying degrees,
the repository needs to store all commits since the project's beginning.
In practice, the CVS repository stores them all as successive diffs.
Thus, even for a very old working copy, CVS is able to calculate the
difference between the working copy's files and the current state of the
repository, and is thereby able to bring the working copy up to date
efficiently. This makes it easy for developers to view the project's
history at any point and to revive even very old working copies.

Although, strictly speaking, the repository could achieve the same
results by other means, in practice, storing diffs is a simple,
intuitive means of implementing the necessary functionality. The
process has the added benefit that, by using patch appropriately, CVS
can reconstruct any previous state of the file tree and thus bring any
working copy from one state to another. It can allow someone to check
out the project as it looked at any particular time. It can also show
the differences, in diff format, between two states of the tree without
affecting someone's working copy.

Thus, the very features necessary to give convenient access to a
project's history are also useful for providing a decentralized,
uncoordinated developer team with the ability to collaborate on the
project.

For now, you can ignore the details of setting up a repository,
administering user access, and navigating CVS-specific file formats
(those will be covered in Repository Administration). For the
moment, we'll concentrate on how to make changes in a working copy.

But first, here is a quick review of terms:

Revision A committed change in the history of a file or set of
files. A revision is one "snapshot" in a constantly changing project.

Repository The master copy where CVS stores a project's full
revision history. Each project has exactly one repository.

Working copy The copy in which you actually make changes to a
project. There can be many working copies of a given project; generally
each developer has his or her own copy.

Check out To request a working copy from the repository. Your
working copy reflects the state of the project as of the moment you
checked it out; when you and other developers make changes, you must use
commit and update to "publish" your changes and view others' changes.

Commit To send changes from your working copy into the central
repository. Also known as check-in.

Log message A comment you attach to a revision when you commit it,
describing the changes. Others can page through the log messages to get
a summary of what's been going on in a project.

Update To bring others' changes from the repository into your
working copy and to show if your working copy has any uncommitted
changes. Be careful not to confuse this with commit; they are
complementary operations. Mnemonic: update brings your working copy up
to date with the repository copy.

Conflict The situation when two developers try to commit changes
to the same region of the same file. CVS notices and points out
conflicts, but the developers must resolve them.

A Day With CVS

This section describes some basic CVS operations, then follows with a
sample session covering typical CVS usage. As the guided tour
progresses, we'll also start to look at how CVS works internally.

Although you don't need to understand every last detail of CVS's
implementation to use it, a basic knowledge of how it works is
invaluable in choosing the best way to achieve a given result. CVS is
more like a bicycle than an automobile, in the sense that its mechanisms
are entirely transparent to anyone who cares to look. As with a
bicycle, you can just hop on and start riding immediately. However, if
you take a few moments to study how the gears work, you'll be able to
ride it much more efficiently. (In the case of CVS, I'm not sure
whether transparency was a deliberate design decision or an accident,
but it does seem to be a property shared by many free programs.
Externally visible implementations have the advantage of encouraging the
users to become contributing developers by exposing them to the system's
inner workings right from the start.)

Each part of the tour may make use of knowledge introduced in previous
parts. Therefore, if this is your first time, I recommend that you
simply start at the beginning and take the tour sequentially, without
skipping over anything. The menu below is merely meant as a convenience
for repeat visitors - you shouldn't use it to jump directly to a
section that interests you unless you're already familiar with the
material in the previous sections.

Conventions Used In This Tour

The tour takes place in a Unix environment. CVS also runs on Windows
and Macintosh operating systems, and Tim Endres of Ice Engineering has
even written a Java client (see http://www.trustice.com/java/jcvs/),
which can be
run anywhere Java runs. However, I'm going to take a wild guess and
assume that the majority of CVS users - present and potential - are
most likely working in a Unix command-line environment. If you aren't
one of these, the examples in the tour should be easy to translate to
other interfaces. Once you understand the concepts, you can sit down at
any CVS front end and work with it (trust me, I've done it many times).

The examples in the tour are oriented toward people who will be using
CVS to keep track of programming projects. However, CVS operations are
applicable to all text documents, not just source code.

The tour also assumes that you already have CVS installed (it's present
by default on many of the popular free Unix systems, so you might
already have it without knowing it) and that you have access to a
repository. Even if you are not set up, you can still benefit from
reading the tour. In Repository Administration, you'll learn how
to install CVS and set up repositories.

Assuming CVS is installed, you should take a moment to find the online
CVS manual. Known familiarly as the "Cederqvist" (after Per Cederqvist,
its original author), it comes with the CVS source distribution and is
usually the most up-to-date reference available. It's written in
Texinfo format and should be available on Unix systems in the "Info"
documentation hierarchy. You can read it either with the command line
info program

floss$ info cvs

or by pressing Ctrl+H and then typing "i" inside Emacs. If neither of
these works for you, consult your local Unix guru (or see
Repository Administration regarding installation issues). You'll
definitely want to have the Cederqvist at your fingertips if you're
going to be using CVS regularly.

Invoking CVS

CVS is one program, but it can perform many different actions: updating,
committing, branching, diffing, and so on. When you invoke CVS, you
must specify which action you want to perform. Thus, the format of a
CVS invocation is:

floss$ cvs command

For example, you can use

floss$ cvs update
floss$ cvs diff
floss$ cvs commit

and so on. (Don't bother to try running any of those particular
commands yet, though; they won't do anything until you're in a working
copy, which we'll get to shortly.)

Both CVS and the command can take options. Options that affect the
behavior of CVS, independently of the command being run, are called
global options; command-specific options are just called command
options. Global options always go to the left of the command; command
options, to its right. So in

floss$ cvs -Q update -p

-Q is a global option, and -p is a command option. (If you're curious,
-Q means "quietly"-that is, suppress all diagnostic output, and print
error messages only if the command absolutely cannot be completed for
some reason; -p means to send the results of update to standard output
instead of to files.)

Accessing A Repository

Before you can do anything, you must tell CVS the location of the
repository you'll be accessing. This isn't a concern if you already
have a working copy checked out - any working copy knows what
repository it came from, so CVS can automatically deduce the repository
for a given working copy. However, let's assume you don't have a
working copy yet, so you need to tell CVS explicitly where to go. This
is done with the -d global option (the -d stands for "directory", an
abbreviation for which there is a historical justification, although -r
for "repository" might have been better), followed by the path to the
repository. For example, assuming the repository is on the local
machine in /usr/local/cvs (a fairly standard location):

floss$ cvs -d /usr/local/cvs command

In many cases, however, the repository is on another machine and must
therefore be reached over the network. CVS provides a choice of network
access methods; which one you'll use depends mostly on the security
needs of the repository machine (hereinafter referred to as "the
server"). Setting up the server to allow various remote access methods
is covered in Repository Administration; here we'll deal only with
the client side.

Fortunately, all the remote access methods share a common invocation
syntax. In general, to specify a remote repository as opposed to a
local one, you just use a longer repository path. You first name the
access method, delimited on each side by colons, followed by the
username and the server name (joined with an @ sign), another separator
colon, and finally the path to the repository directory on the server.

Let's look at the pserver access method, which stands for
"password-authenticated server":

The long repository path following -d told CVS to use the pserver access
method, with the username jrandom, on the server cvs.foobar.com, which
has a CVS repository in /usr/local/cvs. There's no requirement that the
hostname be "cvs.something.com" by the way; that's a common convention,
but it could just as easily have been:

The command actually run was login, which verifies that you are
authorized to work with this repository. It prompts for a password,
then contacts the server to verify the password. Following Unix custom,
cvs login returns silently if the login succeeds; it shows an error
message if it fails (for instance, because the password is incorrect).

You only have to log in once from your local machine to a given CVS
server. After a successful login, CVS stores the password in your home
directory, in a file called .cvspass. It consults that file every time
a repository is contacted via the pserver method, so you only have to
run login the first time you access a given CVS server from a particular
client machine. Of course, you can rerun cvs login anytime if the
password changes.

Note: pserver is currently the only access method requiring an initial
login like this; with the others, you can start running regular CVS
commands immediately.

Once you've stored the authentication information in your .cvspass file,
you can run other CVS commands using the same command-line syntax:

Getting pserver to work in Windows may require an extra step. Windows
doesn't have the Unix concept of a home directory, so CVS doesn't know
where to put the .cvspass file. You'll have to specify a location.
It's normal to designate the root of the C: drive as the home directory:

Any folder in the file system will suffice. You may want to avoid
network drives, though, because the contents of your .cvspass file would
then be visible to anyone with access to the drive.

In addition to pserver, CVS supports the ext method (which uses an
external connection program, such as rsh or ssh), kserver (for the
Kerberos security system version 4), and gserver (which uses the GSSAPI,
or Generic Security Services API, and also handles Kerberos versions 5
and higher). These methods are similar to pserver, but each has its own
idiosyncrasies.

Of these, the ext method is probably the most commonly used. If
you can log into the server with rsh or ssh, you can use the ext
method. You can test it like this:

The first line sets (in Unix Bourne shell syntax) the CVS_RSH
environment variable to rsh, which tells CVS to use the rsh program to
connect. The second line can be any CVS command; you will be prompted
for your password so CVS can log into the server.

If you're in C shell rather than in Bourne shell, try this:

floss% setenv CVS_RSH rsh

and for Windows, try this:

C:\WINDOWS> set CVS_RSH=rsh

The rest of the tour will use the Bourne syntax; translate for your
environment as necessary.

To use ssh (the Secure Shell) instead of rsh, just set the CVS_RSH
variable appropriately:

floss$ CVS_RSH=ssh; export CVS_RSH

Don't get thrown by the fact that the variable's name is CVS_RSH but
you're setting its value to ssh. There are historical reasons for this
(the catch-all Unix excuse, I know). CVS_RSH can point to the name of
any program capable of logging you into the remote server, running
commands, and receiving their output. After rsh, ssh is probably the
most common such program, although there are probably others. Note that
this program must not modify its data stream in any way. This
disqualifies the Windows NT rsh, because it converts (or attempts to
convert) between the DOS and Unix line-ending conventions. You'd have
to get some other rsh for Windows or use a different access method.

The gserver and kserver methods are not used as often as the others and
are not covered here. They're quite similar to what we've covered so
far; see the Cederqvist for details.

If you only use one repository and don't want to type -d repos each
time, just set the CVSROOT environment variable (which perhaps should
have been named CVSREPOS, but it's too late to change that now):

The rest of this tour assumes that you've set CVSROOT to point to your
repository, so the examples will not show the -d option. If you need to
access many different repositories, you should not set CVSROOT and
should just use -d repos when you need to specify the repository.

Starting A New Project

If you're learning CVS in order to work on a project that's already
under CVS control (that is, it is kept in a repository somewhere),
you'll probably want to skip down to the next section, "Checking Out A
Working Copy." On the other hand, if you want to take existing source
code and put it into CVS, this is the section for you. Note that it
still assumes you have access to an existing repository; see
Repository Administration if you need to set up a repository
first.

Putting a new project into a CVS repository is known as importing.
The CVS command, as you may have guessed, is

floss$ cvs import

except that it needs some more options (and needs to be in the right
location) to succeed. First, go into the top-level directory of your
project tree:

This project has two files - README.txt and hello.c - in the top
level, plus two subdirectories - a-subdir and b-subdir - plus some
more files (not shown in the example) inside those subdirectories. When
you import a project, CVS imports everything in the tree, starting from
the current directory and working its way down. Therefore, you should
make sure that the only files in the tree are ones you want to be
permanent parts of the project. Any old backup files, scratch files,
and so on should all be cleaned out.

The general syntax of an import command is

floss$ cvs import -m "log msg" projname vendortag releasetag

The -m flag (for message) is for specifying a short message describing
the import. This will be the first log message for the entire project;
every commit thereafter will also have its own log message. These
messages are mandatory; if you don't give the -m flag, CVS automatically
starts up an editor (by consulting the EDITOR environment variable) for
you to type a log message in. After you save the log message and exit
the editor, the import then continues.

The next argument is the project's name (we'll use "myproj"). This is
the name under which you'll check out the project from the repository.
(What actually happens is that a directory of that name gets created in
the repository, but more on that in Repository Administration.)
The name you choose now does not need to be the same as the name of the
current directory, although in most cases it usually is.

The vendortag and releasetag arguments are a bit of bookkeeping for CVS.
Don't worry about them now; it hardly matters what you use. In
Advanced CVS you'll learn about the rare circumstances where
they're significant. For now, we'll use a username and "start" for
those arguments.

Reading over the output of the import command, you'll notice that CVS
precedes each filename with a single letter - in this case, "N" for
"new file". The use of a single letter on the left to indicate the
status of a file is a general pattern in CVS command output. We'll see
it later in checkout and update as well.

You might think that, having just imported the project, you can start
working in the tree immediately. This is not the case, however. The
current directory tree is still not a CVS working copy. It was the
source for the import command, true, but it wasn't magically changed
into a CVS working copy merely by virtue of having been imported. To
get a working copy, you need to check one out from the repository.

First, though, you might want to archive the current project tree. The
reason is that once the sources are in CVS, you don't want to confuse
yourself by accidentally editing copies that aren't in version control
(because those changes won't become part of the project's history). You
want to do all of your editing in a working copy from now on. However,
you also don't want to remove the imported tree entirely, because you
haven't yet verified that the repository actually has the files. Of
course, you can be 99.999 percent certain that it does because the
import command returned with no error, but why take chances? Paranoia
pays, as every programmer knows. Therefore, do something like this:

Behold - your first working copy! Its contents are exactly the same as
what you imported, with the addition of a subdirectory named "CVS".
That's where CVS stores version control information. Actually, each
directory in the project has a CVS subdirectory:

The fact that CVS keeps its revision information in subdirectories named
CVS means that your project can never contain subdirectories of its own
named CVS. In practice, I've never heard of this being a problem.

Nothing too mysterious there. The Root file points to repository, and
the Repository file points to a project inside the repository. If
that's a little confusing, let me explain.

There is a longstanding confusion about terminology in CVS. The word
"repository" is used to refer to two different things. Sometimes, it
means the root directory of a repository (for example, /usr/local/cvs),
which can contain many projects; this is what the Root file refers to.
But other times, it means one particular project-specific subdirectory
within a repository root (for example, /usr/local/cvs/myproj,
/usr/local/cvs/yourproj, or /usr/local/cvs/fish). The Repository file
inside a CVS subdirectory takes the latter meaning.

In this book, "repository" generally means Root (that is, the top-level
repository), although it may occasionally be used to mean a
project-specific subdirectory. If the intended sense can't be figured
out from the context, there will be clarifying text. Note that the
Repository file may sometimes contain an absolute path to the project
name instead of a relative path. This can make it slightly redundant
with the Root file:

The Entries file stores information about the individual files in the
project. Each line deals with one file, and there are only lines for
files or subdirectories in the immediate parent directory. Here's the
top-level CVS/Entries file in myproj:

and the directory lines are prefixed with "D". (CVS doesn't really keep
a change history for directories, so the fields for revision number and
datestamp are empty.)

The datestamps record the date and time of the last update (in Universal
Time, not local time) of the files in the working copy. That way, CVS
can easily tell whether a file has been modified since the last
checkout, update, or commit. If the file system timestamp differs from
the timestamp in the CVS/Entries file, CVS knows (without even having to
consult the repository) that the file was probably modified.

you can see that the root repository has not changed, but the Repository
file spells out the location of this subdirectory of the project, and
the Entries file contains different lines.

Immediately after import, the revision number of every file in the
project is shown as 1.1.1.1. This initial revision number is a bit of a
special case, so we won't examine it in detail just yet; we'll take a
closer look at revision numbers after we've committed some changes.

Version Versus Revision

The internal revision number that CVS keeps for each file is unrelated
to the version number of the software product of which the files are
part. For example, you may have a project composed of three files,
whose internal revision numbers on May 3, 1999, were 1.2, 1.7, and 2.48.
On that day, you package up a new release of the software and release it
as SlickoSoft Version 3. This is purely a marketing decision and
doesn't affect the CVS revisions at all. The CVS revision numbers are
invisible to your customers (unless you give them repository access);
the only publicly visible number is the "3" in Version 3. You could
have called it Version 1729 as far as CVS is concerned - the version
number (or "release" number) has nothing to do with CVS's internal
change tracking.

To avoid confusion, I'll use the word "revision" to refer exclusively to
the internal revision numbers of files under CVS control. I may still
call CVS a "version control system", however, because "revision control
system" just sounds too awkward.

Making A Change

Let's make the first change to the project since importing it; we'll add
the line

printf ("Goodbye, world!\n");

right after the Hello, world!. Invoke your favorite editor and make the
change:

floss$ emacs hello.c
...

This was a fairly simple change, one where you're not likely to forget
what you did. But in a larger, more complex project, it's quite
possible you may edit a file, be interrupted by something else, and
return several days later and be unable to remember exactly what you
did, or even to remember if you changed anything at all. Which brings
us to our first "CVS Saves Your Life" situation: comparing your working
copy against the repository.

Finding Out What You (And Others) Did - update And diff

Previously, I've talked about updating as a way of bringing changes down
from the repository into your working copy - that is, as a way of
getting other people's changes. However, update is really a bit more
complex; it compares the overall state of the working copy with the
state of the project in the repository. Even if nothing in the
repository has changed since checkout, something in the working copy may
have, and update will show that, too:

The M next to hello.c means the file has been modified since it was last
checked out, and the modifications have not yet been committed to the
repository.

Sometimes, merely knowing which files you've edited is all you need.
However, if you want a more detailed look at the changes, you can get a
full report in diff format. The diff command compares the possibly
modified files in the working copy to their counterparts in the
repository and displays any differences:

That's helpful, if a bit obscure, but there's still a lot of cruft in
the output. For starters, you can ignore most of the first few lines.
They just name the repository file and give the number of the last
checked-in revision. These are useful pieces of information under other
circumstances (we'll look more closely at them later), but you don't
need them when you're just trying to get a sense of what changes have
been made in the working copy.

A more serious impediment to reading the diff is that CVS is announcing
its entry as it goes into each directory during the update. This can be
useful during long updates on large projects, as it gives you a sense of
how much longer the command will take, but right now it's just getting
in the way of reading the diff. Let's tell CVS to be quiet about where
it's working, with the -Q global option:

Better - at least some of the cruft is gone. However, the diff is
still hard to read. It's telling you that at line 6, a new line was
added (that is, what became line 7), whose contents were:

printf ("Goodbye, world!\n");

The preceding ">" in the diff tells you that this line is present in the
newer version of the file but not in the older one.

The format could be made even more readable, however. Most people find
"context" diff format easier to read because it displays a few lines of
context on either side of a change. Context diffs are generated by
passing the -c flag to diff:

Now that's clarity! Even if you're not used to reading context diffs, a
glance at the preceding output will probably make it obvious what
happened: a new line was added (the + in the first column signifies an
added line) between the line that prints Hello, world! and the final
curly brace.

We don't need to be able to read context diffs perfectly (that's patch's
job), but it's worth taking the time to acquire at least a passing
familiarity with the format. The first two lines (after the
introductory cruft) are

and they tell you what is being diffed against what. In this case,
revision 1.1.1.1 of hello.c is being compared against a modified version
of the same file (thus, there's no revision number for the second line,
because only the working copy's changes haven't been committed to the
repository yet). The lines of asterisks and dashes identify sections
farther down in the diff. Later on, a line of asterisks, with a line
number range embedded, precedes a section from the original file. Then
a line of dashes, with a new and potentially different line number range
embedded, precedes a section from the modified file. These sections are
organized into contrasting pairs (known as "hunks"), one side from the
old file and the other side from the new.

The first section of the hunk is empty, meaning that no material was
removed from the original file. The second section shows that, in the
corresponding place in the new file, one line has been added; it's
marked with a "+". (When diff quotes excerpts from files, it reserves
the first two columns on the left for special codes, such as "+" so the
entire excerpt appears to be indented by two spaces. This extra
indentation is stripped off when the diff is applied, of course.)

The line number ranges show the hunk's coverage, including context
lines. In the original file, the hunk was in lines 4 through 7; in the
new file, it's lines 4 through 8 (because a line has been added). Note
that the diff didn't need to show any material from the original file
because nothing was removed; it just showed the range and moved on to
the second half of the hunk.

This diff has two hunks. In the first, five lines were removed (these
lines are only shown in the first section of the hunk, and the second
section's line count shows that it has five fewer lines). An unbroken
line of asterisks forms the boundary between hunks, and in the second
hunk we see that two lines have been added: a blank line and a pointless
comment. Note how the line numbers compensate for the effect of the
previous hunk. In the original file, the second hunk's range of the
area was lines 223 through 228; in the new file, because of the deletion
that took place in the first hunk, the range is in lines 218 through
225.

Congratulations, you are probably now as expert as you'll ever need to
be at reading diffs.

CVS And Implied Arguments

In each of the CVS commands so far, you may have noticed that no files
were specified on the command line. We ran

floss$ cvs diff

instead of

floss$ cvs diff hello.c

and

floss$ cvs update

instead of

floss$ cvs update hello.c

The principle at work here is that if you don't name any files, CVS acts
on all files for which the command could possibly be appropriate. This
even includes files in subdirectories beneath the current directory; CVS
automatically descends from the current directory through every
subdirectory in the tree. For example, if you modified
b-subdir/random.c and a-subdir/subsubdir/fish.c, running update may
result in this:

Note: The -q flag is a less emphatic version of -Q. Had we used -Q, the
command would have printed out nothing at all, because the modification
notices are considered nonessential informational messages. Using the
lowercase -q is less strict; it suppresses the messages we probably
don't want, while allowing certain, more useful messages to pass
through.

In truth, it's more common to run update without restricting it to
certain files. In most situations, you'll want to update the entire
directory tree at once. Remember, the updates we're doing here only
show that some files have been locally modified, because nothing has
changed yet in the repository. When other people are working on the
project with you, there's always the chance that running update will
pull some new changes down from the repository and incorporate them into
your local files. In that case, you may find it slightly more useful to
name which files you want updated.

The same principle can be applied to other CVS commands. For example,
with diff, you can choose to view the changes one file at a time

Committing

The commit command sends modifications to the repository. If you
don't name any files, a commit will send all changes to the repository;
otherwise, you can pass the names of one or more files to be committed
(other files would be ignored, in that case).

Take a moment to read over the output carefully. Most of what it says
is pretty self-explanatory. One thing you may notice is that revision
numbers have been incremented (as expected), but the original revisions
are listed as 1.1 instead of 1.1.1.1 as we saw in the Entries file
earlier.

There is an explanation for this discrepancy, but it's not very
important. It concerns a special meaning that CVS attaches to revision
1.1.1.1. For most purposes, we can just say that files receive a
revision number of 1.1 when imported, but the number is displayed - for
reasons known only to CVS - as 1.1.1.1 in the Entries file, until the
first commit.

Revision Numbers

Each file in a project has its own revision number. When a file is
committed, the last portion of the revision number is incremented by
one. Thus, at any given time, the various files comprising a project
may have very different revision numbers. This just means that some
files have been changed (committed) more often than others.

(You may be wondering, what's the point of the part to the left of the
decimal point, if only the part on the right ever changes? Actually,
although CVS never automatically increments the number on the left, that
number can be incremented on request by a user. This is a rarely used
feature, and we won't cover it in this tour.)

In the example project that we've been using, we just committed changes
to three files. Each of those files is now revision 1.2, but the
remaining files in the project are still revision 1.1. When you check
out a project, you get each file at its highest revision so far. Here
is what qsmith would see if he checked out myproj right now and looked
at the revision numbers for the top-level directory:

Now hello.c is revision 1.3, fish.c and random.c still are revision 1.2,
and every other file is revision 1.1.

Note: that the command was given as cvs ci instead of cvs commit. Most
CVS commands have short forms, to make typing easier. For checkout,
update, and commit, the abbreviated versions are co, up, and ci,
respectively. You can get a list of all of the short forms by running
the command cvs --help-synonyms.

You can usually ignore a file's revision number. In most situations,
the numbers are just internal bookkeeping that CVS handles
automatically. However, being able to find and compare revision numbers
is extremely handy when you have to retrieve (or diff against) an
earlier copy of a file.

Examining the Entries file isn't the only way to discover a revision
number. You can also use the status command

Just ignore the parts of that output that you don't understand. In
fact, that's generally good advice with CVS. Often, the one little bit
of information you're looking for will be accompanied by reams of
information that you don't care about at all, and maybe don't even
understand. This situation is normal. Just pick out what you need, and
don't worry about the rest.

In the previous example, the parts we care about are the first three
lines (not counting the blank line) of each file's status output. The
first line is the most important; it tells you the file's name, and its
status in the working copy. All of the files are currently in sync with
the repository, so they all say Up-to-date. However, if random.c
has been modified but not committed, it might read like this:

The Working revision and Repository revision tell you whether the file
is out of sync with the repository. Returning to our original working
copy (jrandom's copy, which hasn't seen the new change to hello.c yet),
we see:

This tells us that someone has committed a change to hello.c, bringing
the repository copy to revision 1.3, but that this working copy is still
on revision 1.2. The line Status: Needs Patch means that the next update
will retrieve those changes from the repository and "patch" them into
the working copy's file.

Let's pretend for the moment that we don't know anything about qsmith's
change to hello.c, so we don't run status or update. Instead, we just
start editing the file, making a slightly different change at the same
location. This brings us to our first conflict.

meaning that there are changes both in the repository and the working
copy, and these changes need to be merged. (CVS isn't aware that the
changes will conflict, because we haven't run update yet.) When we do
the update, we see this:

Conflicts are always shown delimited by conflict markers, in the
following format:

<<<<<<< (filename)
the uncommitted changes in the working copy
blah blah blah
=======
the new changes that came from the repository
blah blah blah
and so on
>>>>>>> (latest revision number in the repository)

The Entries file also shows that the file is in a halfway state at the
moment:

The way to resolve the conflict is to edit the file so that it contains
whatever text is appropriate, removing the conflict markers in the
process, and then to commit. This doesn't necessarily mean choosing one
change over another; you could decide neither change is sufficient and
rewrite the conflicting section (or indeed the whole file) completely.
In this case, we'll adjust in favor of the first change, but with
capitalization and punctuation slightly different from qsmith's:

Finding Out Who Did What (Browsing Log Messages)

By now, the project has undergone several changes. If you're trying to
get an overview of what has happened so far, you don't necessarily want
to examine every diff in detail. Browsing the log messages would be
ideal, and you can accomplish this with the log command:

floss$ cvs log
(pages upon pages of output omitted)

The log output tends to be a bit verbose. Let's look at the log
messages for just one file:

As usual, there's a lot of information at the top that you can just
ignore. The good stuff comes after each line of dashes, in a format that
is self-explanatory.

When many files are sent in the same commit, they all share the same log
message; a fact that can be useful in tracing changes. For example,
remember back when we committed fish.c and random.c simultaneously? It
was done like this:

The effect of this was to commit both files with the same log message:
"Filled out C code." (As it happened, both files started at revision
1.1 and went to 1.2, but that's just a coincidence. If random.c had
been at revision 1.29, it would have moved to 1.30 with this commit, and
its revision 1.30 would have had the same log message as fish.c's
revision 1.2.)

From this output, you'll know that the two revisions were part of the
same commit (the fact that the timestamps on the two revisions are the
same, or very close, is further evidence).

Browsing log messages is a good way to get a quick overview of what's
been going on in a project or to find out what happened to a specific
file at a certain time. There are also free tools available to convert
raw cvs log output to more concise and readable formats (such as GNU
ChangeLog style); we won't cover those tools in this tour, but they'll
be introduced in Third-Party Tools.

and wonders what jrandom did? In formal terms, the question that qsmith
is asking is, "What's the difference between my revision (1.3) of
hello.c, and jrandom's revision right after it (1.4)?" The way to find
out is with the diff command, but this time by comparing two past
revisions using the -r command option to specify both of them:

The change is pretty clear, when viewed this way. Because the revision
numbers are given in chronological order (usually a good idea), the diff
shows them in order. If only one revision number is given, CVS uses the
revision of the current working copy for the other.

When qsmith sees this change, he instantly decides he likes his way
better and resolves to "undo"-that is, to step back by one revision.

However, this doesn't mean that he wants to lose his revision 1.4.
Although, in an absolute technical sense, it's probably possible to
achieve that effect in CVS, there's almost never any reason to do so.
It's much preferable to keep revision 1.4 in the history and make a new
revision 1.5 that looks exactly like 1.3. That way the undo event
itself is part of the file's history.

The only question is, how can you retrieve the contents of revision 1.3
and put them into 1.5?

In this particular case, because the change is a very simple one, qsmith
can probably just edit the file by hand to mirror revision 1.3 and then
commit. However, if the changes are more complex (as they usually are
in a real-life project), trying to re-create the old revision manually
will be hopelessly error-prone. Therefore, we'll have qsmith use CVS to
retrieve and recommit the older revision's contents.

There are two equally good ways to do this: the slow, plodding way and
the fast, fancy way. We'll examine the slow, plodding way first.

The Slow Method Of Reverting

This method involves passing the -p flag to update, in conjunction with
-r. The -p option sends the contents of the named revision to standard
output. By itself, this isn't terribly helpful; the contents of the
file fly by on the display, leaving the working copy unchanged.
However, by redirecting the standard output into the file, the file will
now hold the contents of the older revision. It's just as though the
file had been hand-edited into that state.

First, though, qsmith needs to get up to date with respect to the
repository:

Oops, there are a few lines of cruft at the beginning. They aren't
actually being sent to standard output, but rather to standard error, so
they're harmless. Nevertheless, they make reading the output more
difficult and can be suppressed with -Q:

Now when update is run, the file is listed as modified, which makes
sense because its contents have changed. Specifically, it has the same
content as the old revision 1.3 (not that CVS is aware of its being
identical to a previous revision - it just knows the file has been
modified). If qsmith wants to make extra sure, he can do a diff to
check:

The Fast Method Of Reverting

The fast, fancy way of reverting is to use the -j (for "join") flag to
the update command. This flag is like -r in that it takes a revision
number, and you can use up to two -j's at once. CVS calculates the
difference between the two named revisions and applies that difference
as a patch to the file in question (so the order in which you give the
revisions is important).

When you only need to revert one file, there's not really much
difference between the plodding and fast methods. Later in the book,
you'll see how the fast method is much better for reverting multiple
files at once. In the meantime, use whichever way you're more
comfortable with.

Reverting Is Not A Substitute For Communication

In all likelihood, what qsmith did in our example was quite rude. When
you're working on a real project with other people and you think that
someone has committed a bad change, the first thing you should do is
talk to him or her about it. Maybe there's a good reason for the change,
or maybe he or she just didn't think things through. Either way, there's
no reason to rush and revert. A full record of everything that happens
is stored permanently in CVS, so you can always revert to a previous
revision after consulting with whoever made the changes.

If you're a project maintainer facing a deadline or you feel you have
the right and the need to revert the change unconditionally, then do so
- but follow it immediately with an email to the author whose change
was reverted, explaining why you did it and what needs to be fixed to
recommit the change.

CVS And Binary Files

Until now, I've left unsaid the dirty little secret of CVS, which is
that it doesn't handle binary files very well (well, there are other
dirty little secrets, but this definitely counts as one of the
dirtiest). It's not that CVS doesn't handle binaries at all; it does,
just not with any great panache.

All the files we've been working with until now have been plain text
files. CVS has some special tricks for text files. For example, when
it's working between a Unix repository and a Windows or Macintosh
working copy, it converts file line endings appropriately for each
platform. For example, Unix convention is to use a linefeed (LF) only,
whereas Windows expects a carriage return/linefeed (CRLF) sequence at
the end of each line. Thus, the files in a working copy on a Windows
machine will have CRLF endings, but a working copy of the same project
on a Unix machine will have LF endings (the repository itself is always
stored in LF format).

Another trick is that CVS detects special strings, known as RCS keyword
strings, in text files and replaces them with revision information and
other useful things. For example, if your file contains this string

$Revision$

CVS will expand on each commit to include the revision number. For
example, it may get expanded to

$Revision: 1.3 $

CVS will keep that string up to date as the file is developed. (The
various keyword strings are documented in Advanced CVS and
Third-Party Tools.)

This string expansion is a very useful feature in text files, as it
allows you to see the revision number or other information about a file
while you're editing it. But what if the file is a JPG image? Or a
compiled executable program? In those kinds of files, CVS could do some
serious damage if it blundered around expanding any keyword string that
it encountered. In a binary, such strings may even appear by
coincidence.

Therefore, when you add a binary file, you have to tell CVS to turn off
both keyword expansion and line-ending conversion. To do so, use -kb:

(In fact, this chapter is one such document, because of the
$Revision$ example shown here.)

Note that you can't meaningfully run cvs diff on two
revisions of a binary file. Diff uses a text-based algorithm that can
only report whether two binary files differ, but not how they differ.
Future versions of CVS may provide a way to diff binary files.

Notice how, in the second and third commands, we name newfile.c
explicitly even though it doesn't exist in the working copy anymore. Of
course, in the commit, you don't absolutely need to name the file, as
long as you don't mind the commit encompassing any other modifications
that may have taken place in the working copy.

Removing Directories

As I said before, CVS doesn't really keep directories under version
control. Instead, as a kind of cheap substitute, it offers certain odd
behaviors that in most cases do the "right thing". One of these odd
behaviors is that empty directories can be treated specially. If you
want to remove a directory from a project, you first remove all the
files in it

The -P option tells update to "prune" any empty directories - that is,
to remove them from the working copy. Once that's done, the directory
can be said to have been removed; all of its files are gone, and the
directory itself is gone (from the working copy, at least, although
there is actually still an empty directory in the repository).

An interesting counterpart to this behavior is that when you run a plain
update, CVS does not automatically bring new directories from the
repository into your working copy. There are a couple of different
justifications for this, none really worth going into here. The short
answer is that from time to time you should run update with the -d flag,
telling it to bring down any new directories from the repository.

For files, that's all there is to it. Renaming directories is not done
very differently: create the new directory, cvs add it, move all the
files from the old directory to the new one, cvs remove them from the
old directory, cvs add them in the new one, cvs commit so everything
takes effect, and then do cvs update -P to make the now-empty directory
disappear from the working copy. That is to say:

Note: the warning message after the third command. It's telling you
that it can't copy olddir's CVS/ subdirectory into newdir because newdir
already has a directory of that name. This is fine, because you want
olddir to keep its CVS/ subdirectory anyway.

Obviously, moving directories around can get a bit cumbersome. The best
policy is to try to come up with a good layout when you initially import
your project so you won't have to move directories around very often.
Later, you'll learn about a more drastic method of moving directories
that involves making the change directly in the repository. However,
that method is best saved for emergencies; whenever possible, it's best
to handle everything with CVS operations inside working copies.

Avoiding Option Fatigue

Most people tire pretty quickly of typing the same option flags with
every command. If you know that you always want to pass the -Q global
option or you always want to use -c with diff, why should you have to
type it out each time?

There is help, fortunately. CVS looks for a .cvsrc file in your home
directory. In that file, you can specify default options to apply to
every invocation of CVS. Here's an example .cvsrc:

diff -c
update -P
cvs -q

If the leftmost word on a line matches a CVS command (in its
unabbreviated form), the corresponding options are used for that command
every time. For global options, you just use cvs. So, for example,
every time that user runs cvs diff, the -c flag is automatically
included.

Getting Snapshots (Dates And Tagging)

Let's return to the example of the program that's in a broken state when
a bug report comes in. The developer suddenly needs access to the
entire project as it was at the time of the last release, even though
many files may have been changed since then, and each file's revision
number differs from the others. It would be far too time-consuming to
look over the log messages, figure out what each file's individual
revision number was at the time of release, and then run update
(specifying a revision number with -r) on each one of them. In medium-
to large-sized projects (tens to hundreds of files), such a process
would be too unwieldy to attempt.

CVS, therefore, provides a way to retrieve previous revisions of the
files in a project en masse. In fact, it provides two ways: by date,
which selects the revisions based on the time that they were committed,
and by tag, which retrieves a previously marked "snapshot" of the
project.

Which method you use depends on the situation. The date-based
retrievals are done by passing update the -D flag, which is similar to
-r but takes dates instead of revision numbers:

With the -D option, update retrieves the highest revision of each file
as of the given date, and it will revert the files in the working copy
to prior revisions if necessary.

When you give the date, you can, and often should, include the time.
For example, the previous command ended up retrieving revision 1.1 of
everything (only three files showed changes, because all of the others
are still at revision 1.1 anyway). Here's the status of hello.c to
prove it:

But a glance back at the log messages from earlier in this chapter shows
that revision 1.2 of hello.c was definitely committed on April 19,
1999. So why did we now get revision 1.1 instead of 1.2?

The problem is that the date "1999-04-19" was interpreted as meaning
"the midnight that begins 1999-04-19" - that is, the very first instant
on that date. This is probably not what you want. The 1.2 commit took
place later in the day. By qualifying the date more precisely, we can
retrieve revision 1.2:

We're almost there. If you look closely at the date/time on the Sticky
Date line, it seems to indicate 4:59:59 A.M., not 11:59 as the command
requested (later we'll get to what the "sticky" means). As you may have
guessed, the discrepancy is due to the difference between local time and
Universal Coordinated Time (also known as "Greenwich mean time"). The
repository always stores dates in Universal Time, but CVS on the client
side usually assumes the local system time zone. In the case of -D,
this is rather unfortunate because you're probably most interested in
comparing against the repository time and don't care about the local
system's idea of time. You can get around this by specifying the GMT
zone in the command:

Nothing happens at all. But you know that there are more recent
versions of at least three files. Why aren't these included in your
working copy?

That's where the "sticky" comes in. Updating ("downdating"?) with the
-D flag causes the working copy to be restricted permanently to that
date or before. In CVS terminology, the working copy has a "sticky
date" set. Once a working copy has acquired a sticky property, it stays
sticky until told otherwise. Therefore, subsequent updates will not
automatically retrieve the most recent revision. Instead, they'll stay
restricted to the sticky date. Stickiness can be revealed by running
cvs status or by directly examining the CVS/Entries file:

CVS would not permit the commit to happen because that would be like
allowing you to go back and change the past. CVS is all about record
keeping and, therefore, will not allow you to do that.

This does not mean CVS is unaware of all the revisions that have been
committed since that date, however. You can still compare the
sticky-dated working copy against other revisions, including future
ones:

This diff reveals that, as of April 19, 1999, the between hello and
goodbye line had not yet been added. It also shows the modification
that we made to the working copy (adding the comment shown in the
preceding code snippet).

You can remove a sticky date (or any sticky property) by updating with
the -A flag (-A stands for "reset", don't ask me why), which brings the
working copy back to the most recent revisions:

Acceptable Date Formats

CVS accepts a wide range of syntaxes to specify dates. You'll never go
wrong if you use ISO 8601 format (that is, the International Standards
Organization standard #8601, see also
www.saqqara.demon.co.uk/datefmt.htm), which is the format used in the
preceding examples. You can also use Internet email dates as described
in RFC 822 and RFC 1123 (see www.rfc-editor.org/rfc/). Finally, you can
use certain unambiguous English constructs to specify dates relative to
the current date.

You will probably never need all of the formats available, but here are
some more examples to give you an idea of what CVS accepts:

The double quotes around the dates are there to ensure that the Unix
shell treats the date as one argument even if it contains spaces. The
quotes will do no harm if the date doesn't contain spaces, so it's
probably best to always use them.

Marking A Moment In Time (Tags)

Retrieving by date is useful when the mere passage of time is your main
concern. But more often what you really want to do is retrieve the
project as it was at the time of a specific event - perhaps a public
release, a known stable point in the software's development, or the
addition or removal of some major feature.

Trying to remember the date when that event took place or deducing the
date from log messages would be a tedious process. Presumably, the
event, because it was important, was marked as such in the formal
revision history. The method CVS offers for making such marks is known
as tagging.

Tags differ from commits in that they don't record any particular
textual change to files, but rather a change in the developers' attitude
about the files. A tag gives a label to the collection of revisions
represented by one developer's working copy (usually, that working copy
is completely up to date so the tag name is attached to the "latest and
greatest" revisions in the repository).

That command associates the symbolic name "Release-1999_05_01" with the
snapshot represented by this working copy. Defined formally, snapshot
means a set of files and associated revision numbers from the project.
Those revision numbers do not have to be the same from file to file and,
in fact, usually aren't. For example, assuming that tag was done on the
same myproj directory that we've been using throughout this chapter and
that the working copy was completely up to date, the symbolic name
"Release-1999_05_01" will be attached to hello.c at revision 1.5, to
fish.c at revision 1.2, to random.c at revision 1.2, and to everything
else at revision 1.1.

It may help to visualize a tag as a path or string linking various
revisions of files in the project. In Figure 2.1, an imaginary string
passes through the tagged revision number of each file in a project.

As you continue to edit files and commit changes, the tag will not move
along with the increasing revision numbers. It stays fixed, "stickily",
at the revision number of each file at the time the tag was made.

Given their importance as descriptors, it's a bit unfortunate that log
messages can't be included with tags or that the tags themselves can't
be full paragraphs of prose. In the preceding example, the tag is
fairly obviously stating that the project was in a releasable state as
of a certain date. However, sometimes you may want to make snapshots of
a more complex state, which can result in ungainly tag names such as:

floss$ cvs tag testing-release-3_pre-19990525-public-release

As a general rule, you should try to keep tags as terse as possible
while still including all necessary information about the event that
you're trying to record. When in doubt, err on the side of being overly
descriptive - you'll be glad later when you're able to tell from some
verbose tag name exactly what circumstance was recorded.

You've probably noticed that no periods or spaces were used in the tag
names. CVS is rather strict about what constitutes a valid tag name.
The rules are that it must start with a letter and contain letters,
digits, hyphens ("-"), and underscores ("_"). No spaces, periods,
colons, commas, or any other symbols may be used.

To retrieve a snapshot by tag name, the tag name is used just like a
revision number. There are two ways to retrieve snapshots: You can
check out a new working copy with a certain tag, or you can switch an
existing working copy over to a tag. Both result in a working copy
whose files are at the revisions specified by the tag.

Most of the time, what you're trying to do is take a look at the project
as it was at the time of the snapshot. You may not necessarily want to
do this in your main working copy, where you presumably have uncommitted
changes and other useful states built up, so let's assume you just want
to check out a separate working copy with the tag. Here's how (but make
sure to invoke this somewhere other than in your existing working copy
or its parent directory!):

We've seen the -r option before in the update command, where it preceded
a revision number. In many ways a tag is just like a revision number
because, for any file, a given tag corresponds to exactly one revision
number (it's illegal, and generally impossible, to have two tags of the
same name in the same project). In fact, anywhere you can use a
revision number as part of a CVS command, you can use a tag name instead
(as long as the tag has been set previously). If you want to diff a
file's current state against its state at the time of the last release,
you can do this:

floss$ cvs diff -c -r Release-1999_05_01 hello.c

And if you want to revert it temporarily to that revision, you can do
this:

floss$ cvs update -r Release-1999_05_01 hello.c

The interchangeability of tags and revision numbers explains some of the
strict rules about valid tag names. Imagine if periods were legal in
tag names; you could have a tag named "1.3" attached to an actual
revision number of "1.47". If you then issued the command

floss$ cvs update -r 1.3 hello.c

how would CVS know whether you were referring to the tag named "1.3", or
the much earlier revision 1.3 of hello.c? Thus, restrictions are placed
on tag names so that they can always be easily distinguished from
revision numbers. A revision number has a period; a tag name
doesn't. (There are reasons for the other restrictions, too, mostly
having to do with making tag names easy for CVS to parse.)

As you've probably guessed by this point, the second method of
retrieving a snapshot - that is, switching an existing working
directory over to the tagged revisions-is also done by updating:

The preceding command is just like the one we used to revert hello.c to
Release-1999_05_01, except that the filename is omitted because
we want to revert the entire project over. (You can, if you want,
revert just one subtree of the project to the tag by invoking the
preceding command in that subtree instead of from the top level,
although you hardly ever would want to do that.)

Note that no files appear to have changed when we updated. The working
copy was completely up to date when we tagged, and no changes had been
committed since the tagging.

However, this does not mean that nothing changed at all. The working
copy now knows that it's at a tagged revision. When you make a change
and try to commit it (let's assume we modified hello.c):

CVS does not permit the commit to happen. (Don't worry about the exact
meaning of that error message yet - we'll cover branches next in this
chapter.) It doesn't matter whether the working copy got to be on a tag
via a checkout or an update. Once it is on a tag, CVS views the working
copy as a static snapshot of a moment in history, and CVS won't let you
change history, at least not easily. If you run cvs status or look at
the CVS/Entries files, you'll see that there is a sticky tag set on each
file. Here's the top level Entries file, for example:

Branches

We've been viewing CVS as a kind of intelligent, coordinating library.
However, it can also be thought of as a time machine (thanks to Jim
Blandy for the analogy). So far, we've only seen how you can examine
the past with CVS, without affecting anything. Like all good time
machines, CVS also allows you to go back in time to change the past.
What do you get then? Science fiction fans know the answer to that
question: an alternate universe, running parallel to ours, but diverging
from ours at exactly the point where the past was changed. A CVS branch
splits a project's development into separate, parallel histories.
Changes made on one branch do not affect the other.

Branching Basics

Why are branches useful?

Let's return for a moment to the scenario of the developer who, in the
midst of working on a new version of the program, receives a bug report
about an older released version. Assuming the developer fixes the
problem, she still needs a way to deliver the fix to the customer. It
won't help to just find an old copy of the program somewhere, patch it
up without CVS's knowledge, and ship it off. There would be no record
of what was done; CVS would be unaware of the fix; and later if
something was discovered to be wrong with the patch, no one would have a
starting point for reproducing the problem.

It's even more ill-advised to fix the bug in the current, unstable
version of the sources and ship that to the customer. Sure, the
reported bug may be solved, but the rest of the code is in a
half-implemented, untested state. It may run, but it's certainly not
ready for prime time.

Because the last released version is thought to be stable, aside from
this one bug, the ideal solution is to go back and correct the bug in
the old release - that is, to create an alternate universe in which the
last public release includes this bug fix.

That's where branches come in. The developer splits off a branch,
rooted in the main line of development (the trunk) not at its most
recent revisions, but back at the point of the last release. Then she
checks out a working copy of this branch, makes whatever changes are
necessary to fix the bug, and commits them on that branch, so there's a
record of the bug fix. Now she can package up an interim release based
on the branch and ship it to the customer.

Her change won't have affected the code on the trunk, nor would she want
it to without first finding out whether the trunk needs the same bug fix
or not. If it does, she can merge the branch changes into the trunk.
In a merge, CVS calculates the changes made on the branch between the
point where it diverged from the trunk and the branch's tip (its most
recent state), then applies those differences to the project at the tip
of the trunk. The difference between the branch's root and its tip
works out, of course, to be precisely the bug fix.

Another good way to think of a merge is as a special case of updating.
The difference is that in a merge, the changes to be incorporated are
derived by comparing the branch's root and tip, instead of by comparing
the working copy against the repository.

The act of updating is itself similar to receiving patches directly from
their authors and applying them by hand. In fact, to do an update, CVS
calculates the difference (that's "difference" as in the diff program)
between the working copy and the repository and then applies that diff
to the working copy just as the patch program would. This mirrors the
way in which a developer takes changes from the outside world, by
manually applying patch files sent in by contributors.

Thus, merging the bug fix branch into the trunk is just like accepting
some outside contributor's patch to fix the bug. The contributor would
have made the patch against the last released version, just as the
branch's changes are against that version. If that area of code in the
current sources hasn't changed much since the last release, the merge
will succeed with no problems. If the code is now substantially
different, however, the merge will fail with conflict (that is, the
patch will be rejected), and some manual fiddling will be necessary.
Usually this is accomplished by reading the conflicting area, making the
necessary changes by hand, and committing. Figure 2.3 shows a picture
of what happens in a branch and merge.

(branch on which bug was fixed)
.---------------->---------------.
/ |
/ |
/ |
/ |
/ V (<------ point of merge)
====*===================================================================>
(main line of development)
[Figure 2.3: A branch and then a merge. Time flows left to right.]

We'll now walk through the steps necessary to make this picture happen.
Remember that it's not really time that's flowing from left to right in
the diagram, but rather the revision history. The branch will not have
been made at the time of the release, but is created later, rooted back
at the release's revisions.

In our case, let's assume the files in the project have gone through
many revisions since they were tagged as Release-1999_05_01, and
perhaps files have been added as well. When the bug report regarding
the old release comes in, the first thing we'll want to do is create a
branch rooted at the old release, which we conveniently tagged
Release-1999_05_01.

One way to do this is to first check out a working copy based on that
tag, then create the branch by re-tagging with the -b (branch) option:

Take a good look at that last command. It may seem somewhat arbitrary
that tag is used to create branches, but there's actually a reason for
it: The tag name will serve as a label by which the branch can be
retrieved later. Branch tags do not look any different from non-branch
tags, and are subject to the same naming restrictions. Some people like
to always include the word branch in the tag name itself (for example,
Release-1999_05_01-bugfix-branch), so they can distinguish branch
tags from other kinds of tags. You may want to do this if you find
yourself often retrieving the wrong tag.

(And while we're at it, note the -d myproj_old_release option to
checkout in the first CVS command. This tells checkout to put the
working copy in a directory called myproj_old_release, so we won't
confuse it with the current version in myproj. Be careful not to
confuse this use of -d with the global option of the same name, or with
the -d option to update.)

Of course, merely running the tag command does not switch this working
copy over to the branch. Tagging never affects the working copy; it
just records some extra information in the repository to allow you to
retrieve that working copy's revisions later on (as a static piece of
history or as a branch, as the case may be).

Retrieval can be done one of two ways (you're probably getting used to
this motif by now!). You can check out a new working copy on the branch

The end result is the same (well, the name of the new working copy's
top-level directory may be different, but that's not important for CVS's
purposes). If your current working copy has uncommitted changes, you'll
probably want to use checkout instead of update to access the branch.
Otherwise, CVS attempts to merge your changes into the working copy as
it switches it over to the branch. In that case, you might get
conflicts, and even if you didn't, you'd still have an impure branch.
It won't truly reflect the state of the program as of the designated
tag, because some files in the working copy will contain modifications
made by you.

Anyway, let's assume that by one method or another you get a working
copy on the desired branch:

A closer look reveals that each file's revision number is just the
branch number (as shown on the Sticky Tag line) plus an extra
digit on the end.

What you're seeing is a little bit of CVS's inner workings. Although
you almost always use a branch to mark a project-wide divergence, CVS
actually records the branch on a per-file basis. This project had five
files in it at the point of the branch, so five individual branches were
made, all with the same tag name: Release-1999_05_01-bugfixes.

Most people consider this per-file scheme a rather inelegant
implementation on CVS's part. It's a bit of the old RCS legacy showing
through-RCS didn't know how to group files into projects, and even
though CVS does, it still uses code inherited from RCS to handle
branches.

Ordinarily, you don't need to be too concerned with how CVS is keeping
track of things internally, but in this case, it helps to understand the
relationship between branch numbers and revision numbers. Let's look at
the hello.c file; everything I'm about to say about hello.c applies to
the other files in the branch (with revision/branch numbers adjusted
accordingly).

The hello.c file was on revision 1.5 at the point where the branch was
rooted. When we created the branch, a new number was tacked onto the
end to make a branch number (CVS chooses the first unused even, nonzero
integer). Thus, the branch number in this case became 1.5.2.
The branch number by itself is not a revision number, but it is the root
(that is, the prefix) of all the revision numbers for hello.c along this
branch.

However, when we ran that first CVS status in a branched working copy,
hello.c's revision number showed up as only 1.5, not
1.5.2.0 or something similar. This is because the initial
revision on a branch is always the same as the trunk revision of the
file, where the branch sprouts off. Therefore, CVS shows the trunk
revision number in status output, for as long as the file is the same on
both branch and trunk.

Once we had committed a new revision, hello.c was no longer the same on
both trunk and branch - the branch incarnation of the file had changed,
while the trunk remained the same. Accordingly, hello.c was assigned
its first branch revision number. We saw this in the status output
after the commit, where its revision number is clearly 1.5.2.1.

The same story applies to the random.c file. Its revision number at the
time of branching was 1.2, so its first branch is 1.2.2,
and the first new commit of random.c on that branch received the
revision number 1.2.2.1.

There is no numeric relationship between 1.5.2.1 and
1.2.2.1 - no reason to think that they are part of the same
branch event, except that both files are tagged with
Release-1999_05_01-bugfixes, and the tag is attached to branch
numbers 1.5.2 and 1.2.2 in the respective files.
Therefore, the tag name is your only handle on the branch as a
project-wide entity. Although it is perfectly possible to move a file
to a branch by using the revision number directly

floss$ cvs update -r 1.5.2.1 hello.c
U hello.c
floss$

it is almost always ill-advised. You would be mixing the branch
revision of one file with non-branch revisions of the others. Who knows
what losses may result? It is better to use the branch tag to refer to
the branch and do all files at once by not specifying any particular
file. That way you don't have to know or care what the actual branch
revision number is for any particular file.

It is also possible to have branches that sprout off other branches, to
any level of absurdity. For example, if a file has a revision number of
1.5.4.37.2.3, its revision history can be diagrammed like this:

Admittedly, only the rarest circumstances make such a branching depth
necessary, but isn't it nice to know that CVS will go as far as you're
willing to take it? Nested branches are created the same way as any
other branch: Check out a working copy on branch N, run cvs tag
-b branchname in it, and you'll create branch N.M in the
repository (where N represents the appropriate branch revision
number in each file, such as 1.5.2.1, and M represents the
next available branch at the end of that number, such as 2).

Merging Changes From Branch To Trunk

Now that the bug fix has been committed on the branch, let's switch the
working copy over to the highest trunk revisions and see if the bug fix
needs to be done there, too. We'll move the working copy off the branch
by using update -A (branch tags are like other sticky properties in this
respect) and then diffing against the branch we just left:

The diff shows that good-bye is spelled with a hyphen in the branch
revision of hello.c, and that the trunk revision of that file has a
comment near the end that the branch revision doesn't have. Meanwhile,
in random.c, the branch revision has a capital "A" and a period, whereas
the trunk doesn't.

To actually merge the branch changes into the current working copy, run
update with the -j flag (the same j for "join" that we used to revert a
file to an old revision before):

This takes the changes from the branch's root to its tip and merges them
into the current working copy (which subsequently shows those
modifications just as though the files had been hand-edited into that
state). The changes are then committed onto the trunk, since nothing in
the repository changed when a working copy underwent a merge.

Although no conflicts were encountered in this example, it's quite
possible (even probable) that there would be some in a normal merge. If
that happens, they need to be resolved like any other conflict, and then
committed.

Multiple Merges

Sometimes a branch will continue to be actively developed even after the
trunk has undergone a merge from it. For example, this can happen if a
second bug in the previous public release is discovered and has to be
fixed on the branch. Maybe someone didn't get the joke in random.c, so
on the branch, you have to add a line explaining it

As you can see, that didn't have quite the desired effect-we got a
conflict, even though the trunk copy hadn't been modified there and,
therefore, no conflict was expected.

The trouble was that the update command behaved exactly as described: It
tried to take all the changes between the branch's root and tip and
merge them into the current working copy. The only problem is, some of
those changes had already been merged into this working copy. That's
why we got the conflict:

You could go through resolving all such conflicts by hand-it's usually
not hard to tell what you need to do in each file. Nevertheless, it is
even better to avoid a conflict in the first place. By passing two -j
flags instead of one, you'll get only those changes from where you last
merged to the tip instead of all of the changes on the branch, from root
to tip. The first -j gives the starting point on the branch, and the
second is just the plain branch name (which implies the tip of the
branch).

The question then is, how can you specify the point on the branch from
which you last merged? One way is to qualify by using a date along with
the branch tag name. CVS provides a special syntax for this:

If the branch tag name is followed by a colon and then a date (in any of
the usual CVS date syntaxes), CVS will include only changes later than
that date. So if you knew that the original bug fix was committed on
the branch three days ago, the preceding command would merge the second
bug fix only.

A better way, if you plan ahead, is to tag the branch after each bug fix
(just a regular tag - we're not starting a new branch here or anything
like that). Suppose after fixing the bug in the branch and committing,
you do this in the branch's working copy:

This way, of course, is much better than trying to recall how long ago
you made one change versus another, but it only works if you remember to
tag the branch every time it is merged to the trunk. The lesson,
therefore, is to tag early and tag often! It's better to err on the side
of too many tags (as long as they all have descriptive names) than to
have too few. In these last examples, for instance, there was no
requirement that the new tag on the branch have a name similar to the
branch tag itself. Although I named it
Release-1999_05_01-bugfixes-fix-number-1, it could just as easily
have been fix1. However, the former is preferable, because it
contains the name of the branch and thus won't ever be confused with a
tag on some other branch. (Remember that tag names are unique within
files, not within branches. You can't have two tags named fix1
in the same file, even if they refer to revisions on different
branches.)

Creating A Tag Or Branch Without A Working Copy

As stated earlier, tagging affects the repository, not the working copy.
That begs the question: Why require a working copy at all when tagging?
The only purpose that it serves is to designate which project and which
revisions of the various files in the project are being tagged. If you
could specify the project and revisions independently of the working
copy, no working copy would be necessary.

There is such a way: the rtag command (for "repository tag"). It's very
similar to tag; a couple of examples will explain its usage. Let's go
back to the moment when the first bug report came in and we needed to
create a branch rooted at the last public release. We checked out a
working copy at the release tag and then ran tag -b on it:

floss$ cvs tag -b Release-1999_05_01-bugfixes

This created a branch rooted at Release-1999_05_01. However,
because we know the release tag, we could have used it in an rtag
command to specify where to root the branch, not even bothering with a
working copy:

That's all there is to it. That command can be issued from anywhere,
inside or outside a working copy. However, your CVSROOT environment
variable would have to point to the repository, of course, or you can
specify it with the global -d option. It works for non-branch tagging,
too, but it's less useful that way because you have to specify each
file's revision number, one by one. (Or you can refer to it by tag, but
then you'd obviously already have a tag there, so why would you want to
set a second one on the exact same revisions?)

You now know enough to get around in CVS and probably enough to start
working with other people on a project. There are still a few minor
features that haven't been introduced, as well as some unmentioned but
useful options to features already seen. These will all be presented as
appropriate in chapters to come, in scenarios that will demonstrate both
how and why to use them. When in doubt, don't hesitate to consult the
Cederqvist manual; it is an indispensable resource for serious CVS
users.

Repository Administration

In An Overview of CVS, you learned enough CVS to use it
effectively as a project participant. If you're going to be a project
maintainer, however, you'll need to know how to install CVS and
administer repositories. In this chapter, we'll throw back the curtain
and look in detail at how the repository is structured, and how CVS uses
it. You'll learn all the major steps CVS goes through during updates
and commits, and how you can modify its behavior. By understanding how
CVS works, you'll also be able to trace problems to their causes, and
fix them in maintainable ways.

This may sound very involved, but remember that CVS has already proven
quite long-lived, and will probably be around for many years to come.
Whatever you learn now will be useful for a long time. CVS also tends
to become more indispensable the more you use it. If you're going to be
that dependent on something (and trust me, you are), it's worth really
getting to know it.

With that in mind, let's begin at the beginning: putting CVS on your
system.

Getting And Installing CVS

In many cases, you won't have to go out and get CVS, because it will
already be on your system. If you run one of the major Linux or FreeBSD
distributions, it's probably already installed in /usr/bin or some other
likely location. If not, Red Hat Linux users can usually find an RPM
(Red Hat Package) for the latest, or nearly latest, version of CVS in
their distributions. And Debian users can install the latest Debian
package with these commands:

floss$ apt-get update
floss$ apt-get install cvs

If CVS isn't already on your machine, you'll probably have to build it
from source. If you're a non-Unix user, you'll probably find it easier
to get a prebuilt binary for your operating system (more on that later).
Fortunately, CVS is fully autoconfiscated - that is, it uses the
GNU autoconfiguration mechanism, making compilation from source
surprisingly easy.

Getting And Building CVS Under Unix

As of this writing, there are two canonical sites from which you can
download CVS. One is the Free Software Foundation's FTP site,
ftp://ftp.gnu.org/gnu/cvs/, which offers CVS as an official GNU
tool. The other is Cyclic Software's download site. Cyclic Software
is, if not the maintainer of CVS, then the "maintainer of the
maintainers", by providing a repository server and download access for
users and developers. They distribute releases from
http://download.cyclic.com/pub/.

Either location is fine. In the following example, I use Cyclic
Software's site. If you point your FTP client (probably your Web
browser) there, you'll see a list of directories, something like this:

Pay attention to the directories beginning with "cvs-" (you can ignore
most of the others). There are three such directories, which means that
you're already faced with a choice: Get the designated "stable" release,
or go with a newer (but less-tested) interim release. The stable
releases have only one decimal point, as in "cvs-1.10", whereas the
interim releases have minor version increments tacked on the end, as in
"1.10.5".

The GNU site usually only offers the major releases, not the interim
ones, so you won't see all of this if you get CVS from there. In
general, the interim releases have been pretty safe, and sometimes
contain fixes to bugs that were found in the major release. Your best
policy is to go with the highest interim release, but if you encounter
any problems with it, be prepared to drop back to the previous release,
as many times as necessary. The highest release listed in the earlier
example is cvs-1.10.6. Entering that directory, we see this:

Index of /pub/cvs-1.10.6
cvs-1.10.6.tar.gz 17-May-99 08:44 2.2M

That's it - the full source code to CVS. Just download it to your
machine, and you're ready to build. At this point, if you're already
familiar with the standard build process for GNU tools, you know what to
do and probably don't need to read anything between here and the section
Anatomy Of A CVS Distribution. On the other hand, if you're not
sure how to proceed, then read on....

The following compilation instructions and examples assume that you have
a fairly standard distribution of Unix. Any of the free versions of
Unix (for example, FreeBSD or Linux) should work with no problem, as
should the major commercial Unix versions (such as SunOS/Solaris, AIX,
HP-UX, or Ultrix). Even if these instructions don't work for you
exactly as written, don't give up hope. Although covering the details
of compiling on every operating system is beyond the scope of this book,
I'll give some pointers to other help resources later in this chapter.

Now you have a new directory on your machine - cvs-1.10.6 - and it is
populated with the CVS source code. Go into that directory and
configure CVS for your system, by using the provided configure script:

When the configure command finishes, the source tree will know
everything it needs to know about compiling on your machine. The next
step is to type:

floss$ make

You'll see lots of output fly by, then type:

floss$ make install

You'll see yet more output fly by; when it's all over, CVS will be
installed on your system. (You will probably need to do that last step
as the superuser.)

By default, the CVS executable will end up as /usr/local/bin/cvs.
This assumes you have a decent make program installed on your system
(again, if you don't have one, get the GNU project's make from
ftp://ftp.gnu.org/gnu/make/).

If you want CVS to install to a location other than /usr/local/bin, you
should change how you run the initial configuration step. For example,

floss$ ./configure --prefix=/usr

results in CVS being installed as /usr/bin/cvs (it always ends up as
PREFIX/bin/cvs). The default prefix is /usr/local, which is fine for
most installations.

Note To Experienced Users: Although older versions of CVS consisted of
more than just an executable in that they depended on having RCS
installed as well, this has not been the case since Version 1.10.
Therefore, you don't need to worry about any libraries or executables
other than cvs itself.

If you just intend to use CVS to access remote repositories, the
preceding is all you need to do. If you also plan to serve a repository
from this system, a few additional steps are necessary, which are
covered later in this chapter.

Getting And Installing CVS Under Windows

Unless you're truly religious about having the source code to your
executable, you don't need to compile CVS from source on your Windows
box. Unlike Unix, the necessary compilation tools probably do not
already exist on your system, so a source build would involve first
going out and getting those tools. Because such a project is beyond the
scope of this book, I'll just give instructions for getting a
precompiled CVS binary.

First, note that Windows binary distributions of CVS are usually made
only for major releases of CVS - not for the interim releases - and
are not found on the GNU FTP site. So you'll need to go to Cyclic
Software's download site, where in the major version directory,
http://download.cyclic.com/pub/cvs-1.10/, you'll see an extra
subdirectory

Index of /pub/cvs-1.10
cvs-1.10.tar.gz 14-Aug-98 09:35 2.4M
windows/

inside of which is a ZIP file:

Index of /pub/cvs-1.10/windows
cvs-1.10-win.zip 14-Aug-98 10:10 589k

This ZIP file contains a binary distribution of CVS. Download and
extract that ZIP file:

The README there contains detailed instructions. For most
installations, they can be summarized as follows: Put all of the EXE and
DLL files in a directory in your PATH. Additionally, if you're going to
be using the pserver method to access a remote repository, you may need
to put the following in your C:\AUTOEXEC.BAT file and reboot:

set HOME=C:

This tells CVS where to store the .cvspass file.

CVS running under Windows cannot currently serve repositories to remote
machines; it can be a client (connecting to remote repositories), and
operate in local mode (using a repository on the same machine). For the
most part, this book assumes that CVS under Windows is operating as a
client. However, it shouldn't be too hard to set up a local repository
under Windows after reading the Unix-oriented instructions in the rest
of this chapter.

If you are only accessing remote repositories, you may not even need to
run CVS. There is a tool called WinCvs that implements only the
client-side portion of CVS. It is distributed separately from CVS
itself but, like CVS, is freely available under the GNU General Public
License. More information is available from http://www.wincvs.org.

Frankly, I have no idea which one is best. Try them all, not
necessarily in the order given, and see which one you like. MacCVS Pro
seems to be under active development. MacCvs is apparently a companion
project of WinCVS and shares a home page with it. (As of this writing, a
notice on the WinCVS page states, "Development of MacCvs will be resumed
soon.", whatever that means.)

Limitations Of The Windows And Macintosh Versions

The Windows and Macintosh distributions of CVS are generally limited in
functionality. They can all act as clients, meaning that they can
contact a repository server to obtain a working copy, commit, update,
and so on. But they can't serve repositories themselves. If you set it
up right, the Windows port can use a local-disk repository, but it still
can't serve projects from that repository to other machines. In
general, if you want to have a network-accessible CVS repository, you
must run the CVS server on a Unix box.

Anatomy Of A CVS Distribution

The preceding instructions are designed to get you up and running
quickly, but there's a lot more inside a CVS source distribution than
just the code. Here's a quick road map to the source tree, so you'll
know which parts are useful resources and which can be ignored.

Informational Files

In the top level of the distribution tree, you'll find several files
containing useful information (and pointers to further information).
They are, in approximate order of importance:

NEWS - This file lists the changes from one release to the next,
in reverse chronological order (that is, most recent first). If you've
already been using CVS for a while and have just upgraded to a new
version, you should look at the NEWS file to see what new features are
available. Also, although most changes to CVS preserve backward
compatibility, noncompatible changes do occur from time to time. It's
better to read about them here than be surprised when CVS doesn't behave
the way you expect it to.

BUGS - This file contains exactly what you think it does: a list
of known bugs in CVS. They usually aren't show-stoppers, but you should
read over them whenever you install a new release.

DEVEL-CVS - This file is the CVS "constitution". It describes
the process by which changes are accepted into the main CVS distribution
and the procedures through which a person becomes a CVS developer. You
don't really need to read it if you just want to use CVS; however, it's
highly interesting if you want to understand how the mostly
uncoordinated efforts of people scattered across the globe coalesce into
a working, usable piece of software. And of course, it's required
reading if you plan to submit a patch (be it a bug fix or new feature)
to CVS.

HACKING - Despite its name, the HACKING file doesn't say much
about the design or implementation of CVS. It's mainly a guide to
coding standards and other technical administrivia for people thinking
of writing a patch to CVS. It can be thought of as an addendum to the
DEVEL-CVS file. After you understand the basic philosophy of CVS
development, you must read the HACKING file to translate that into
concrete coding practices.

FAQ - This is the CVS "Frequently Asked Questions" document.
Unfortunately it has a rather spotty maintenance history. David Grubbs
took care of it until 1995, then he (presumably) got too busy and it
languished for a while. Eventually, in 1997, Pascal Molli took over
maintenance. Molli also didn't have time to maintain it by hand, but at
least he found time to put it into his automated FAQ-O-Matic system,
which allows the public to maintain the FAQ in a decentralized manner
(basically, anyone can edit or add entries via a Web form). This was
probably a good thing, in that at least the FAQ was once again being
maintained; however, its overall organization and quality control are
not on the same level as if a person were maintaining it.

The master version of the FAQ is always available from Molli's Web site
(http://www.loria.fr/~molli/cvs-index.html, under the link
"Documentation"). The FAQ file shipped with CVS distributions is
generated automatically from that FAQ-O-Matic database, so by the time
it reaches the public it's already a little bit out of date.
Nevertheless, it can be quite helpful when you're looking for hints and
examples about how to do something specific (say, merging a large branch
back into the trunk or resurrecting a removed file). The best way to
use it is as a reference document; you can bring it up in your favorite
editor and do text searches on terms that interest you. Trying to use
it as a tutorial would be a mistake - it's missing too many important
facts about CVS to serve as a complete guide.

Subdirectories

The CVS distribution contains a number of subdirectories. In the course
of a normal installation, you won't have to navigate among them, but if
you want to go poking around in the sources, it's nice to know what each
one does. Here they are:

The majority of these can be ignored. The emx/, os2/, vms/, and
windows-NT/ subdirectories all contain operating-system-specific source
code, which you would only need if you're actually trying to debug a
code-level problem in CVS (an unlikely situation, though not unheard
of). The diff/ and zlib/ subdirectories contain CVS's internal
implementations of the diff program and the GNU gzip compression
library, respectively. (CVS uses the latter to reduce the number of bits
it has to send over the network when accessing remote repositories.)

The contrib/ and tools/ subdirectories contain free third-party software
meant to be used with CVS. In contrib/, you will find an assortment of
small, specialized shell scripts (read contrib/README to find out what
they do). The tools/ subdirectory used to contain contributed software,
but now contains a README file, which says in part:

This subdirectory formerly contained tools that can be used with CVS.
In particular, it used to contain a copy of pcl-cvs version 1.x.
Pcl-cvs is an Emacs interface to CVS.
If you are looking for pcl-cvs, we'd suggest pcl-cvs version 2.x, at:
ftp://ftp.weird.com/pub/local/

The PCL-CVS package it's referring to is very handy, and I'll have more
to say about it in Third-Party Tools.

The src/ and lib/ subdirectories contain the bulk of the CVS source
code, which involves the CVS internals. The main data structures and
commands are implemented in src/, whereas lib/ contains small code
modules of general utility that CVS uses.

The man/ subdirectory contains the CVS man pages (intended for the Unix
online manual system). When you ran make install, they were
incorporated into your Unix system's regular man pages, so you can type

floss$ man cvs

and get a rather terse introduction and subcommand reference to CVS.
Although useful as a quick reference, the man pages may not be as up to
date or complete as the Cederqvist manual (see the next section);
however, the man pages are more likely to be incomplete than actually
wrong, if it's any comfort.

The Cederqvist Manual

That leaves the doc/ subdirectory, whose most important inhabitant is
the famed Cederqvist. These days, it's probably a stretch to call
it "the Cederqvist". Although Per Cederqvist (of Signum Support,
Linkoping Sweden, www.signum.se) wrote the first version around 1992, it
has been updated since then by many other people. For example, when
contributors add a new feature to CVS, they usually also document it in
the Cederqvist.

The Cederqvist manual is written in Texinfo format, which is used by the
GNU project because it's relatively easy to produce both online and
printed output from it (in Info and PostScript formats, respectively).
The Texinfo master file is doc/cvs.texinfo, but CVS distributions come
with the Info and PostScript pregenerated, so you don't have to worry
about running any Texinfo tools yourself.

Although the Cederqvist can be used as an introduction and tutorial, it
is probably most useful as a reference document. For that reason, most
people browse it online instead of printing it out (although the
PostScript file is doc/cvs.ps, for those with paper to spare).
If this is the first time you've installed CVS on your system, you'll
have to take an extra step to make sure the manual is accessible online.

The Info files (doc/cvs.info, doc/cvs.info-1, doc/cvs.info-2, and so on)
were installed for you when you ran make install. Although the files
were copied into the system's Info tree, you may still have to add a
line for CVS to the Info table of contents, the "Top" node. (This will
only be necessary if this is the first time CVS has been installed on
your system; otherwise, the entry from previous installations should
already be in the table of contents.)

If you've added new Info documentation before, you may be familiar with
the process. First figure out where the Info pages were installed. If
you used the default installation (in /usr/local/), then the Info files
are /usr/local/info/cvs.info*. If you installed using

floss$ ./configure --prefix=/usr

the files ended up as /usr/info/cvs.*. After you locate the files,
you'll need to add a line for CVS to the Info table of contents, which
is in a file named dir in that directory (so in the latter case, it
would be /usr/info/dir). If you don't have root access, ask your system
administrator to do it. Here is an excerpt from dir before the
reference to CVS documentation was added:

The format of the line is very important. You must include the
asterisk, spaces, and colon in * Cvs: and the parentheses and
period in (cvs). after it. If any of these elements are missing,
the Info dir format will be corrupt, and you'll be unable to read the
Cederqvist.

Once the manual is installed and referred to from the table of contents,
you can read it with any Info-compatible browser. The ones most likely
to be installed on a typical Unix system are either the command-line
Info reader, which can be invoked this way if you want to go straight to
the CVS pages

floss$ info cvs

and the one within Emacs, which is invoked by typing

M-x info

or

C-h i

Take whatever time is necessary to get the Cederqvist set up properly on
your system when you install CVS; it will pay off many times down the
road when you need to look something up.

Other Sources Of Information

In addition to the Cederqvist, the FAQ, and the other files in the
distribution itself, there are Internet resources devoted to CVS. If
you're going to administrate a CVS server, you'll probably want to join
the info-cvs mailing list. To subscribe, send email to
[email protected] (the list itself is
[email protected]). Traffic can be medium to heavy, around 10
to 20 emails a day, most of them questions seeking answers. The
majority of these can be deleted without reading (unless you want to
help people by answering their questions, which is always nice), but
every now and then someone will announce the discovery of a bug or
announce a patch that implements some feature you've been wanting.

You can also join the formal bug report mailing list, which includes
every bug report sent in. This probably isn't necessary, unless you
intend to help fix the bugs, which would be great, or you're
terrifically paranoid and want to know about every problem other people
find with CVS. If you do want to join, send email to
[email protected].

There's also a Usenet newsgroup, comp.software.config-mgmt, which
is about version control and configuration management systems in
general, in which there is a fair amount of discussion about CVS.

Finally, there are at least three Web sites devoted to CVS. Cyclic
Software's http://www.cyclic.com has been CVS's informal home
site for a few years, and probably will continue to be for the
foreseeable future. Cyclic Software also provides server space and Net
access for the repository where the CVS sources are kept. The Cyclic
Web pages contain comprehensive links to experimental patches for CVS,
third-party tools that work with CVS, documentation, mailing list
archives, and just about everything else. If you can't find what you
need in the distribution, http://www.cyclic.com is the place to
start looking.

Two other good sites are Pascal Molli's
http://www.loria.fr/~molli/cvs-index.html and Sean Dreilinger's
http://durak.org/cvswebsites/. The biggest attraction at Molli's
site is, of course, the FAQ, but it also has links to CVS-related tools
and mailing list archives. Dreilinger's site specializes in information
about using CVS to manage Web documents and also has a CVS-specific
search engine.

Starting A Repository

Once the CVS executable is installed on your system, you can start using
it right away as a client to access remote repositories, following the
procedures described in An Overview of CVS. However, if you want
to serve revisions from your machine, you have to create a repository
there. The command to do that is

floss$ cvs -d /usr/local/newrepos init

where /usr/local/newrepos is a path to wherever you want the
repository to be (of course, you must have write permission to that
location, which may imply running the command as the root user). It may
seem somewhat counterintuitive that the location of the new repository
is specified before the init subcommand instead of after it, but by
using the -d option, it stays consistent with other CVS commands.

The command will return silently after it is run. Let's examine the new
directory:

The single subdirectory in the new repository - CVSROOT/ - contains
various administrative files that control CVS's behavior. Later on,
we'll examine those files one by one; for now, the goal is just to get
the repository working. In this case, "working" means users can import,
check out, update, and commit projects.

Don't confuse the CVSROOT environment variable introduced in An Overview of CVS with this CVSROOT subdirectory in the repository. They
are unrelated - it is an unfortunate coincidence that they share the
same name. The former is a way for users to avoid having to type
-d <repository-location> every time they use CVS; the latter
is the administrative subdirectory of a repository.

Once the repository is created, you must take care of its permissions.
CVS does not require any particular, standardized permission or file
ownership scheme; it merely needs write access to the repository.
However - partly for security reasons, but mainly for your own sanity
as an administrator - I highly recommend that you take the following
steps:

Add a Unix group cvs to your system. Any users who need to
access the repository should be in this group. For example, here's the
relevant line from my machine's /etc/group file:

cvs:*:105:kfogel,sussman,jimb,noel,lefty,fitz,craig,anonymous,jrandom

Make the repository's group ownership and permissions reflect this new
group:

Now any of the users listed in that group can start a project by running
cvs import, as described in An Overview of CVS.
Checkout, update, and commit should work as well. They can also reach
the repository from remote locations by using the :ext: method,
assuming that they have rsh or ssh access to the repository
machine. (You may have noticed that the chgrp and chmod commands in that
example gave write access to a user named anonymous, which is not
what one would expect. The reason is that even anonymous, read-only
repository users need system-level write access, so that their CVS
processes can create temporary lockfiles inside the repository. CVS
enforces the "read-only" restriction of anonymous access not through
Unix file permissions, but by other means, which will be covered in
Anonymous Access.)

If your repository is intended to serve projects to the general public,
where contributors won't necessarily have accounts on the repository
machine, you should set up the password-authenticating server now
(see The Password-Authenticating Server). It's necessary for
anonymous read-only access, and it's also probably the easiest way to
grant commit access to certain people without giving them full accounts
on the machine.

The Password-Authenticating Server

Before running through the steps needed to set up the password server,
let's examine how such connections work in the abstract. When a remote
CVS client uses the :pserver: method to connect to a repository,
the client is actually contacting a specific port number on the server
machine - specifically, port number 2401 (which is 49 squared, if you
like that sort of thing). Port 2401 is the designated default port for
the CVS pserver, although one could arrange for a different port to be
used as long as both client and server agree on it.

The CVS server is not actually waiting for connections at that port -
the server won't get started up until a connection actually arrives.
Instead, the Unix inetd (InterNET Daemon) program is listening on that
port, and needs to know that when it receives a connection request
there, it should start up the CVS server and connect it to the incoming
client.

This is accomplished by modifying inetd's configuration files:
/etc/services and /etc/inetd.conf. The services file maps
raw port numbers to service names and then inetd.conf tells inetd what
to do for a given service name.

First, put a line like this into /etc/services (after checking to make
sure it isn't already there):

Now, restart inetd so it notices the changes to its configuration files
(if you don't know how to restart the daemon, just reboot the machine -
that will work too).

That's enough to permit connections, but you'll also want to set up
special CVS passwords - separate from the users' regular login
passwords - so people can access the repository without compromising
overall system security.

The CVS password file is CVSROOT/passwd in the repository. It was not
created by default when you ran cvs init, because CVS doesn't know for
sure that you'll be using pserver. Even if the password file had been
created, CVS would have no way of knowing what usernames and passwords
to create. So, you'll have to create one yourself; here's a sample
CVSRoot/passwd file:

The extra colon followed by an optional system username tells CVS that
connections authenticated with USERNAME should run as the system account
SYSTEM_USERNAME - in other words, that CVS session would only be able
to do things in the repository that someone logged in as SYSTEM_USERNAME
could do.

If no system username is given, USERNAME must match an actual login
account name on the system, and the session will run with that user's
permissions. In either case, the encrypted password should not be the
same as the user's actual login password. It should be an independent
password used only for CVS pserver connections.

The password is encrypted using the same algorithm as the standard Unix
system passwords stored in /etc/passwd. You may be wondering at this
point, how does one acquire an encrypted version of a password? For
Unix system passwords, the passwd command takes care of the encryption
in /etc/passwd for you. Unfortunately, there is no corresponding cvs
passwd command (it has been proposed several times, but no one's gotten
around to writing it - perhaps you'll do it?).

This is an inconvenience, but only a slight one. If nothing else, you
can always temporarily change a regular user's system password using
passwd, cut and paste the encrypted text from /etc/passwd into
CVSROOT/passwd, and then restore the old password (note that on some
systems, the encrypted passwords are found in /etc/shadow and are
readable only by root.)

That scheme is workable but rather cumbersome. It would be much easier
to have a command-line utility that takes a plain text password as its
argument and outputs the encrypted version. Here is such a tool,
written in Perl:

They could then type some text as their password and thereafter
be able to execute CVS commands with the same access privileges as the
system user craig.

If someone attempts to authenticate with a username and password that
don't appear in CVSROOT/passwd, CVS will check to see if that username
and password are present in /etc/passwd. If they are (and if the
password matches, of course), CVS will grant access. It behaves this
way for the administrator's convenience, so that separate CVSROOT/passwd
entries don't have to be set up for regular system users. However, this
behavior is also a security hole, because it means that if one of those
users does connect to the CVS server, her regular login password will
have crossed over the network in cleartext, potentially vulnerable to
the eyes of password sniffers. A bit further on, you'll learn how to
turn off this "fallback" behavior, so that CVS consults only its own
passwd file. Whether you leave it on or off, you should probably force
any CVS users who also have login accounts to maintain different
passwords for the two functions.

Although the passwd file authenticates for the whole repository, with a
little extra work you can still use it to grant project-specific access.
Here's one method:

Suppose you want to grant some remote developers access to project
foo, and others access to project bar, and you don't want
developers from one project to have commit access to the other. You can
accomplish this by creating project-specific user accounts and groups on
the system and then mapping to those accounts in the CVSROOT/passwd
file.

Some of the CVS usernames map onto the system user account
cvs-foo and some onto cvs-bar. Because CVS runs under the
user ID of the system account, you just have to make sure that the
relevant parts of the repository are writeable only by the appropriate
users and groups. If you just make sure that the user accounts are
locked down pretty tight (no valid login password, /bin/false as
the shell), then this system is reasonably secure (but see later in this
chapter about CVSROOT permissions!). Also, CVS does record changes and
log messages under the CVS username, not the system username, so you can
still tell who is responsible for a given change.

Anonymous Access

So far we've only seen how to use the password-authenticating server to
grant normal full access to the repository (although admittedly one can
restrict that access through carefully arranged Unix file permissions).
Turning this into anonymous, read-only access is a simple step: You just
have to add a new file, or possibly two, in CVSROOT/. The files' names
are readers and writers - the former containing a list of
usernames who can only read the repository, the latter users who can
read and write.

If you list a username in CVSROOT/readers, that user will have only read
access to all projects in the repository. If you list a username in
CVSROOT/writers, that user will have write access, and every pserver
user not listed in writers will have read-only access (that is, if the
writers file exists at all, it implies read-only access for all those
not listed in it). If the same username is listed in both files, CVS
resolves the conflict in the more conservative way: the user will have
read-only access.

The format of the files is very simple: one user per line (don't forget
to put a newline after the last user). Here is a sample readers file:

anonymous
splotnik
guest
jbrowse

Note that the files apply to CVS usernames, not system usernames. If
you use user aliasing in the CVSROOT/passwd file (putting a system
username after a second colon), the leftmost username is the one to list
in a readers or writers file.

Just to be painfully accurate about it, here is a formal description of
the server's behavior in deciding whether to grant read-only or
read-write access:

If a readers file exists and this user is listed in it, then she gets
read-only access. If a writers file exists and this user is not listed
in it, then she also gets read-only access (this is true even if a
readers file exists but that person is not listed there). If that
person is listed in both, she gets read-only access. In all other
cases, that person gets full read-write access.

Thus, a typical repository with anonymous CVS access has this (or
something like it) in CVSROOT/passwd

And, of course, the aforementioned setup in /etc/services and
/etc/inetd.conf. That's all there is to it!

Note that some older Unix systems don't support usernames longer than
eight characters. One way to get around this would be to call the user
anon instead of anonymous in CVSROOT/passwd and in the
system files, because people often assume that anon is short for
anonymous anyway. But it might be better to put something like this
into the CVSROOT/passwd file

anonymous:XR4EZcEs0szik:cvsanon

(and then of course use cvsanon in the system files). That way,
you'd be able to publish a repository address that uses
anonymous, which is more or less standard now. People accessing
the repository with

Repository Structure

The new repository still has no projects in it. Let's re-run the
initial import from An Overview of CVS, watching what happens to
the repository. (For simplicity's sake, all commands will assume that
the CVSROOT environment variable has been set to /usr/local/newrepos, so
there's no need to specify the repository with -d on imports and
checkouts.)

Before the import, the repository contained only its administrative
area, CVSROOT. After the import, a new directory - myproj -
appeared. The files and subdirectories inside that new directory look
suspiciously like the project we imported, except that the files have
the suffix ,v. These are RCS-format version control files (the
,v stands for "version"), and they are the backbone of the
repository. Each RCS file stores the revision history of its
corresponding file in the project, including all branches and tags.

RCS Format

You do not need to know any of the RCS format to use CVS (although there
is an excellent writeup included with the source distribution, see
doc/RCSFILES). However, a basic understanding of the format can be of
immense help in troubleshooting CVS problems, so we'll take a brief peek
into one of the files, hello.c,v. Here are its contents:

Whew! Most of that you can ignore; don't worry about the relationship
between 1.1 and 1.1.1.1, for example, or the implied 1.1.1 branch -
they aren't really significant from a user's or even an administrator's
point of view. What you should try to grok is the overall format. At
the top is a collection of header fields:

If you look closely, you'll see that the first revision's contents are
stored under the heading 1.1, but that the log message there is "Initial
revision", whereas the log message we actually used at import time was
"initial import into CVS", which appears farther down, under
Revision 1.1.1.1. You don't need to worry about this discrepancy
right now. It happens because imports are a special circumstance: In
order to make repeated imports into the same project have a useful
effect, import actually places the initial revision on both the main
trunk and on a special branch (the reasons for this will become clearer
when we look at vendor branches in Advanced CVS). For now, you
can treat 1.1 and 1.1.1.1 as the same thing.

The file becomes even more revealing after we commit the first
modification to hello.c:

Now the full contents of Revision 1.2 are stored in the file, and the
text for Revision 1.1 has been replaced with the cryptic formula:

d7 1

The d7 1 is a diff code that means "starting at line 7,
delete 1 line". In other words, to derive Revision 1.1, delete line 7
from Revision 1.2! Try working through it yourself. You'll see that it
does indeed produce Revision 1.1 - it simply does away with the line we
added to the file.

This demonstrates the basic principle of RCS format: It stores only the
differences between revisions, thereby saving a lot of space compared
with storing each revision in full. To go backwards from the most
recent revision to the previous one, it patches the later revision using
the stored diff. Of course, this means that the further back you travel
in the revision history, the more patch operations must be performed
(for example, if the file is on Revision 1.7 and CVS is asked to
retrieve Revision 1.4, it has to produce 1.6 by patching backwards from
1.7, then 1.5 by patching 1.6, then 1.4 by patching 1.5). Fortunately,
old revisions are also the ones least often retrieved, so the RCS system
works out pretty well in practice: The more recent the revision, the
cheaper it is to obtain.

As for the header information at the top of the file, you don't need to
know what all of it means. However, the effects of certain operations
show up very clearly in the headers, and a passing familiarity with them
may prove useful.

When you commit a new revision on the trunk, the head label is
updated (note how it became 1.2 in the preceding example, when the
second revision to hello.c was committed). When you add a file as
binary or tag it, those operations are recorded in the headers as well.
As an example, we'll add foo.jpg as a binary file and then tag it a
couple of times:

Notice the b in the expand line at the end - it's due to our having
used the -kb flag when adding the file, and means the file won't undergo
any keyword or newline expansions, which would normally occur during
checkouts and updates if it were a regular text file. The tags appear
in the symbols section, one tag per line - both of them are attached to
the first revision, since that's what was tagged both times. (This also
helps explain why tag names can only contain letters, numbers, hyphens,
and underscores. If the tag itself contained colons or dots, the RCS
file's record of it might be ambiguous, because there would be no way to
find the textual boundary between the tag and the revision to which it
is attached.)

RCS Format Always Quotes @ Signs

The @ symbol is used as a field delimiter in RCS files, which
means that if one appears in the text of a file or in a log message, it
must be quoted (otherwise, CVS would incorrectly interpret it as marking
the end of that field). It is quoted by doubling - that is, CVS always
interprets @@ as "literal @ sign", never as "end of current
field". When we committed foo.jpg, the log message was

The only reason you should care is that if you ever find yourself
hand-editing RCS files (a rare circumstance, but not unheard of), you
must remember to use double @ signs in revision contents and log
messages. If you don't, the RCS file will be corrupt and will probably
exhibit strange and undesirable behaviors.

Speaking of hand-editing RCS files, don't be fooled by the permissions
in the repository:

(For those not fluent in Unix ls output, the -r--r--r-- lines on
the left essentially mean that the files can be read but not changed.)
Although the files appear to be read-only for everyone, the directory
permissions must also be taken into account:

The myproj/ directory itself - and its subdirectories - are all
writeable by the owner (jrandom) and the group (users). This means that
CVS (running as jrandom, or as anyone in the users group) can create and
delete files in those directories, even if it can't directly edit files
already present. CVS edits an RCS file by making a separate copy of it,
so you should also make all of your changes in a temporary copy, and
then replace the existing RCS file with the new one. (But please don't
ask why the files themselves are read-only - there are historical
reasons for that, having to do with the way RCS works when run as a
standalone program.)

Incidentally, having the files' group be users is probably not
what you want, considering that the top-level directory of the
repository was explicitly assigned group cvs. You can correct
the problem by running this command inside the repository:

floss$ cd /usr/local/newrepos
floss$ chgrp -R cvs myproj

The usual Unix file-creation rules govern which group is assigned to new
files that appear in the repository, so once in a while you may need to
run chgrp or chmod on certain files or directories in the repository
(setting the SGID bit with chmod g+s is often a good
strategy: it makes children of a directory inherit the directory's group
ownership, which is usually what you want in the repository). There are
no hard and fast rules about how you should structure repository
permissions; it just depends on who is working on what projects.

What Happens When You Remove A File

When you remove a file from a project, it doesn't just disappear. CVS
must be able to retrieve such files when you request an old snapshot of
the project. Instead, the file gets put in the Attic, literally:

In each repository directory of a project, the presence of an
Attic/ subdirectory means that at least one file has been removed
from that directory (this means that you shouldn't use directories named
Attic in your projects). CVS doesn't merely move the RCS file into
Attic/, however; it also commits a new revision into the file, with a
special revision state of dead. Here's the relevant section from
Attic/foo.jpg,v:

There's a lot more to know about RCS format, but this is sufficient for
a CVS adminstrator to maintain a repository. It's quite rare to
actually edit an RCS file; you'll usually just have to tweak file
permissions in the repository, at least if my own experience is any
guide. Nevertheless, when CVS starts behaving truly weirdly (rare, but
not completely outside the realm of possibility), you may want to
actually look inside the RCS files to figure out what's going on.

The CVSROOT/ Administrative Directory

The files in newrepos/CVSROOT/ are not part of any project, but are used
to control CVS's behavior in the repository. The best way to edit those
files is to check out a working copy of CVSROOT, just like a regular
project:

We'll take the files in their approximate order of importance. Note
that each of the files comes with an explanatory comment at the
beginning (the comment convention is the same across all of them: A
# sign at the beginning of the line signifies a comment, and CVS
ignores such lines when parsing the files). Remember that any change
you make to the administrative files in your checked out working copy
won't affect CVS's behavior until you commit the changes.

If you're extremely security conscious, you may want to arrange the
Unix-level permissions on CVSROOT to be different from permissions
elsewhere in the repository, in order to have fine-grained control over
who can commit changes to CVSROOT. As you'll see a little later, being
able to modify the files in CVSROOT essentially gives any CVS user -
even remote ones - the ability to run arbitrary commands on the
repository machine.

The config File

The config file allows you to configure certain global behavioral
parameters. It follows a very strict format

PARAMETER=VALUE
(etc)

with no extra spaces allowed. For example, here is a possible config
file:

SystemAuth=yes
TopLevelAdmin=no
PreservePermissions=no

(An absent entry would be equivalent to no.)

The SystemAuth parameter governs whether CVS should look in the
system passwd file if it fails to find a given username in the
CVSROOT/passwd file. CVS distributions are shipped with this set to
no to be conservative about your system's security.

TopLevelAdmin tells CVS whether to make a sibling CVS/ directory
when it checks out a working copy. This CVS/ directory would not be
inside the working copy, but rather next to it. It might be convenient
to turn this on if you tend (and your repository's users tend) to check
out many different projects from the same repository. Otherwise, you
should leave it off, as it can be disconcerting to see an extra CVS/
directory appear where you don't expect it.

PreservePermissions governs whether to preserve file permissions
and similar metadata in the revision history. This is a somewhat
obscure feature that probably isn't worth describing in detail. See the
node Special Files in the Cederqvist if you're interested
(node is Texinfo-speak for a particular location within an Info
document. To go to a node while reading Info, just type g
followed by the name of the node, from anywhere inside the document).

LockDir is also a rarely used feature. In special circumstances,
you may want to tell CVS to create its lockfiles somewhere other than
directly in the project subdirectories, in order to avoid permission
problems. These lockfiles keep CVS from tripping over itself when
multiple operations are performed on the same repository directory
simultaneously. Generally, you never need to worry about them, but
sometimes users may have trouble updating or checking out from a
repository directory because they're unable to create a lockfile (even
on read-only operations, CVS needs to create a lockfile to avoid
situations where it could end up reading while another invocation of CVS
is writing). The usual fix for this is to change repository
permissions, but when that's not feasible, the LockDir parameter can
come in handy.

There are no other parameters at this time, but future versions of CVS
may add new ones; you should always check the Cederqvist or the
distribution config file itself for updates.

Notice how in both cases the module's name became the name of the
directory created for the working copy. In the case of asub, it didn't
even bother with the intermediate myproj/ directory, but created a
top-level asub/ instead, even though it came from myproj/a-subdir in the
repository. Updates, commits, and all other CVS commands will behave
normally in those working copies - the only thing unusual about them
are their names.

By putting file names after the directory name, you can define a module
consisting of just some of the files in a given repository directory.
For example

You can define a module that will include multiple repository
directories by using the -a (for alias) flag, but note that the
directories will get them checked out under their original names. For
example, this line

twoproj -a myproj yourproj

would allow you to do this (assuming that both myproj/ and yourproj/ are
in the repository):

The name twoproj was a convenient handle to pull in both
projects, but it didn't affect the names of the working copies. (There
is no requirement that alias modules refer to multiple directories, by
the way; we could have omitted twoproj, in which case myproj would still
have been checked out under the name myproj.)

Modules can even refer to other modules, by prefixing them with an
ampersand:

mp myproj
asub myproj/a-subdir
twoproj -a myproj yourproj
tp &twoproj

Doing a checkout of tp would have exactly the same result as the
checkout of twoproj did.

There are a few other tricks you can do with modules, most of them less
frequently used than the ones just presented. See the node modules in
the Cederqvist for information about them.

The commitinfo And loginfo And rcsinfo Files

Most of the other administrative files provide programmatic hooks
into various parts of the commit process (for example, the ability to
validate log messages or file states before permitting the commit, or
the ability to notify a group of developers whenever a commit happens in
a certain directory of the repository).

The files generally share a common syntax. Each line is of the form:

REGULAR_EXPRESSION PROGRAM_TO_RUN

The regular expression will be tested against the directory into which
the commit is taking place (with the directory name relative to the top
of the repository). If it matches, the designated program will be run.
The program will be passed the names of each of the files in the commit;
it can do whatever it likes with those names, including opening up the
files and examining their contents. If the program returns with a
nonzero exit status, the commit is prevented from taking place.

(Regular expressions are a system for concisely describing classes
of strings. If you aren't familiar with regular expressions, you can
get by with the following short summary: foo would match any file
whose name contains the string foo; and foo.*bar would
match any file whose name contains foo, followed by any number of
characters, followed by the string bar. That's because normal
substrings match themselves, but . and * are special.
. matches any character, and * means match any number of
the preceding character, including zero. The ^ and $
signs mean match at the beginning and end of the string, respectively;
thus, ^foo.*bar.*baz$ would match any string beginning with
foo, containing bar somewhere in the middle, and ending
with baz. That's all we'll go into here; this summary is a very
abbreviated subset of full regular expression syntax.)

The commitinfo file is for generic hooks you want run on every
commit. Here are some example commitinfo lines:

So any commit into myproj/a-subdir/ would match the first line, which
would then run the check-asubdir.sh script. A commit in any project
whose name (actual repository directory name, not necessarily module
name) contained the string ou would run the validate-project.pl
script, unless the commit had already matched the previous a-subdir
line.

In place of a regular expression, the word DEFAULT or ALL
may be used. The DEFAULT line (or the first DEFAULT line, if there are
more than one) will be run if no regular expression matches, and each of
the ALL lines will be run in addition to any other lines that may match.

The file names passed to the program do not refer to RCS files - they
point to normal files, whose contents are exactly the same as the
working-copy files being committed. The only unusual aspect is that CVS
has them temporarily placed inside the repository, so they'll be
available to programs running on the machine where the repository is
located.

The loginfo file is similar to commitinfo, except that instead of
acting on the files' contents, it acts on the log message. The left
side of the loginfo file contains regular expressions, including
possibly DEFAULT and ALL lines. The program invoked on the right side
receives the log message on its standard input; it can do whatever it
wants with that input.

The program on the right side can also take an arbitrary number of
command-line arguments. One of those arguments can be a special
% code, to be expanded by CVS at runtime, as follows:

%s ------> name(s) of the file(s) being committed
%V ------> revision number(s) before the commit
%v ------> revision number(s) after the commit

The expansion always begins with the repository subdirectory (relative
to the top of the repository), followed by the per-file information.
For example, if the files committed were foo, bar, and baz, all in
myproj/a-subdir, then %s would expand into

myproj/a-subdir foo bar baz

whereas %V would expand to show their old revision numbers

myproj/a-subdir 1.7 1.134 1.12

and %v their new revision numbers:

myproj/a-subdir 1.8 1.135 1.13

You can combine % expressions by enclosing them in curly braces
following % sign - this will expand them into a series of
comma-separated sublists, each containing the corresponding information
for one file in the commit. For instance, %{sv} would expand
to

myproj/a-subdir foo,1.8 bar,1.135 baz,1.13

and %{sVv} would expand to

myproj/a-subdir foo,1.7,1.8 bar,1.134,1.135 baz,1.12,1.13

(You may have to look carefully to distinguish the commas from the
periods in those examples.)

In the first line, any commit in the myproj subdirectory of the
repository invokes log.pl, passing it an email address (to which
log.pl will send a mail containing the log message), followed by
the repository, followed by all the files in the commit.

In the second line, any commit in a repository subdirectory containing
the string ou will invoke the (imaginary) ou-notify.pl
script, passing it the repository followed by the file names and new
revision numbers of the files in the commit.

The third line invokes the (equally imaginary) default-notify.pl
script for any commit that didn't match either of the two previous
lines, passing it all possible information (path to repository, file
names, old revisions, and new revisions).

The verifymsg And rcsinfo Files

Sometimes you may just want a program to automatically verify that the
log message conforms to a certain standard and to stop the commit if
that standard is not met. This can be accomplished by using
verifymsg, possibly with some help from rcsinfo.

The verifymsg file is the usual combination of regular expressions
and programs. The program receives the log message on standard input;
presumably it runs some checks to verify that the log message meets
certain criteria, then it exits with status zero or nonzero. If the
latter, the commit will fail.

Meanwhile, the left side of rcsinfo has the usual regular expressions,
but the right side points to template files instead of programs. A
template file might be something like this

Condition:
Fix:
Comments:

or some other collection of fields that a developer is supposed to fill
out to form a valid log message. The template is not very useful if
everyone commits using the -m option explicitly, but many developers
prefer not to do that. Instead, they run

floss$ cvs commit

and wait for CVS to automatically fire up a text editor (as specified in
the EDITOR environment variable). There they write a log message, then
save the file and exit the editor, after which CVS continues with the
commit.

In that scenario, an rcsinfo template would insert itself into the
editor before the user starts typing, so the fields would be displayed
along with a reminder to fill them in. Then when the user commits, the
appropriate program in verifymsg is invoked. Presumably, it will
check that the message does follow that format, and its exit status will
reflect the results of its inquiry (with zero meaning success).

As an aid to the verification programs, the path to the template from
the rcsinfo file is appended as the last argument to the program command
line in verifymsg; that way, the program can base its
verification process on the template itself, if desired.

Note that when someone checks out a working copy to a remote machine,
the appropriate rcsinfo template file is sent to the client as well
(it's stored in the CVS/ subdirectory of the working copy). However,
this means that if the rcsinfo file on the server is changed after that,
the client won't see the changes without re-checking out the project
(merely doing an update won't work).

Note also that in the verifymsg file, the ALL keyword is not supported
(although DEFAULT still is). This is to make it easier to override
default verification scripts with subdirectory-specific ones.

The taginfo File

What loginfo does for log messages, taginfo does for tags. The left
side of taginfo is regular expressions, as usual, and the right side is
programs. Each program is automatically handed arguments when CVS tag
is invoked, in this order:

We haven't covered the -F option to tag before now, but it's exactly
what the above implies: a way to move a tag from one revision to
another. For example, if the tag Known_Working is attached to
Revision 1.7 of a file and you want it attached to Revision 1.11
instead, you'd do this

cvs tag -r 1.11 -F Known_Working foo.c

which removes the tag from 1.7, or wherever it was previously in that
file, and puts it at 1.11.

The cvswrappers File

The redundantly-named cvswrappers file gives you a way to specify that
certain files should be treated as binary, based on their file name.
CVS does not assume that all .jpg files are JPG image data, for example,
so it doesn't automatically use -kb when adding JPG files. Nonetheless,
certain projects would find it very useful to simply designate all JPG
files as binary. Here is a line in cvswrappers to do that:

*.jpg -k 'b'

The b is separate and in quotes because it's not the only
possible RCS keyword expansion mode; one could also specify o,
which means not to expand $ sign keywords but to do newline
conversion. However, b is the most common parameter.

There are a few other modes that can be specified from the wrappers
file, but they're for such rare situations that they're probably not
worth documenting here (translation: your author has never had to use
them). See the node Wrappers in the Cederqvist if you're
curious.

The notify File

This file is used in conjunction with CVS's watch features, which
are described in Advanced CVS. Nothing about it will make sense
until you understand what watches are (they're a useful but
non-essential feature), so see Advanced CVS for details about this
file and about watches.

CVS only pays attention to the working versions, not the RCS files, when
it's looking for guidance on how to behave. Therefore, whenever you
commit your working copy of CVSROOT/ (which might, after all, even be
checked out to a different machine), CVS automatically updates any
changed files in the repository itself. You will know that this has
happened because CVS will print a message at the end of such commits:

CVS automatically knows about the standard administrative files, and
will rebuild them in CVSROOT/ as necessary. If you decide to put custom
files in CVSROOT/ (such as programs or rcsinfo template files), you'll
have to tell CVS explicitly to treat them the same way.

That's the purpose of the checkoutlist file. It has a different format
from most of the files we've looked at so far

FILENAME ERROR_MESSAGE_IF_FILE_CANNOT_BE_CHECKED_OUT

for example,

log.pl unable to check out / update log.pl in CVSROOT
bugfix.tmpl unable to check out / update bugfix.tmpl in CVSROOT

Certain files in CVSROOT are traditionally not kept under revision
control. One such is the history file, which keeps a running
record of all actions in the repository, for use by the cvs history command (which lists checkout, update, and tag activity for a
given file or project directory). Incidentally, if you just remove the
history file, CVS will obligingly stop keeping that log.

Note: sometimes the history file is the cause of permission problems,
and the easiest way to solve them is to either make it world-writeable
or just remove it.

Another unrevisioned administrative file is passwd, the
assumption being that having it checked out over the network might
compromise the passwords (even though they're encrypted). You'll have
to decide based on your own security situation whether you want to add
passwd to checkoutlist or not; by default, it is not in checkoutlist.

Two final notes about the CVSROOT/ directory: It is possible, if you
make a big enough mistake, to commit an administrative file that is
broken in such a way as to prevent any commits from happening at all.
If you do that, naturally you won't be able to commit a fixed version of
the administrative file! The solution is to go in and hand-edit the
repository's working copy of the administrative file to correct the
problem; the whole repository may stay inaccessible until you do that.

Also, for security's sake, make sure your CVSROOT/ directory is only
writeable by users you trust (by trust, I mean you trust both
their intentions and their ability not to compromise their password).
The *info files give people the ability to invoke arbitrary
programs, so anyone who can commit or edit files in the CVSROOT/
directory can essentially run any command on the system. That's
something you should always keep in mind.

Commit Emails

The loginfo file is how one sets up commit emails - automated emails
that go out to everyone working on a project whenever a commit takes
place. (It may seem counterintuitive that this is done in loginfo
instead of commitinfo, but the point is that one wants to include the
log message in the email). The program to do the mailing -
contrib/log.pl in the CVS source distribution - can be installed
anywhere on your system. I customarily put it in the repository's
CVSROOT/ subdirectory, but that's just a matter of taste.

You may need to edit log.pl a bit to get it to work on your
system, possibly changing the first line to point to your Perl
interpreter, and maybe changing this line

$mailcmd = "| Mail -s 'CVS update: $modulepath'";

to invoke your preferred mailer, which may or may not be named
Mail. Once you've got it set the way you like it, you can put
lines similar to these into your loginfo:

The %s expands to the names of the files being committed; the -f
option to log.pl takes a file name, to which the log message will
be appended (so CVSROOT/commitlog is an ever-growing file of log
messages); and the -m flag takes an email address, to which
log.pl will send a message about the commit. The address is
usually a mailing list, but you can specify the -m option as many times
as necessary in one log.pl command line.

Finding Out More

Although this chapter tries to give a complete introduction to
installing and administering CVS, I've left out things that are either
too rarely used to be worth mentioning or already well documented in the
Cederqvist manual. The latter category includes setting up the other
remote access methods: RSH/SSH, kserver (Kerberos 4), and GSSAPI (which
includes Kerberos 5, among other things). It should be noted that
nothing special needs to be done for RSH/SSH connections, other than
making sure that the user in question can log into the repository
machine using RSH or SSH. If they can and CVS is installed on both
client and server, and they have the right permissions to use the
repository directly from the server machine, then they should be able to
access the repository remotely via the :ext: method.

Descriptions of certain specialized features of CVS have been deferred
to later chapters, so they can be introduced in contexts where their
usefulness is obvious. General CVS troubleshooting tips are found in
Tips And Troubleshooting. Although it's not necessary to read the
entire Cederqvist manual, you should familiarize yourself with it; it
will be an invaluable reference tool. If for some reason you don't have
Info working on your machine and don't want to print the manual, you can
browse it online at http://durak.org/cvswebsites/doc/ or
http://www.loria.fr/~molli/cvs/doc/cvs_toc.html.

Advanced CVS

Now that we've covered the basic concepts of CVS usage and repository
administration, we'll look at how CVS can be incorporated into the
entire process of development. The fundamental CVS working cycle -
checkout, update, commit, update, commit, and so on - was demonstrated
by the examples in An Overview of CVS. This chapter elaborates on
the cycle and discusses how CVS can be used to help developers
communicate, give overviews of project activity and history, isolate and
reunite different branches of development, and automate frequently
performed tasks. Some of the techniques covered introduce new CVS
commands, but many merely explain better ways to use commands that you
already know.

Watches (CVS As Telephone)

A major benefit of using CVS on a project is that it can function as a
communications device as well as a record-keeper. This section
concentrates on how CVS can be used to keep participants informed about
what's going on in a project. As is true with other aspects of CVS,
these features reward cooperation. The participants must want to be
informed; if people choose not to use the communications features,
there's nothing CVS can do about it.

How Watches Work

In its default behavior, CVS treats each working copy as an isolated
sandbox. No one knows what you're doing in your working copy until you
commit your changes. In turn, you don't know what others are doing in
theirs - except via the usual methods of communication, such as
shouting down the hallway, "Hey, I'm going to work on parse.c now. Let
me know if you're editing it so we can avoid conflicts!"

This informality works for projects where people have a general idea of
who's responsible for what. However, this process can break down when a
large number of developers are active in all parts of a code base and
want to avoid conflicts. In such cases, they frequently have to cross
each others' areas of responsibility but can't shout down the hallway at
each other because they're geographically distributed.

A feature of CVS called watches provides developers with a way to
notify each other about who is working on what files at a given time.
By "setting a watch" on a file, a developer can have CVS notify her if
anyone else starts to work on that file. The notifications are normally
sent via email, although it is possible to set up other notification
methods.

To use watches, you must modify one or two files in the repository
administrative area, and developers must add some extra steps to the
usual checkout/update/commit cycle. The changes on the repository side
are fairly simple: You may need to edit the CVSROOT/notify file
so that CVS knows how notifications are to be performed. You may also
have to add lines to the CVSROOT/users file, which supplies
external email addresses.

On the working copy side, developers have to tell CVS which files they
want to watch so that CVS can send them notifications when someone else
starts editing those files. They also need to tell CVS when they start
or stop editing a file, so CVS can send out notifications to others who
may be watching. The following commands are used to implement these
extra steps:

cvs watch

cvs edit

cvs unedit

The command watch differs from the usual CVS command pattern in
that it requires further subcommands, such as cvs watch add..., cvs watch remove..., and so on.

In the following example, we'll look at how to turn on watches in the
repository and then how to use watches from the developer's side. The
two example users, jrandom and qsmith, each have their own separate
working copies of the same project; the working copies may even be on
different machines. As usual, all examples assume that the $CVSROOT
environment variable has already been set, so there's no need to pass -d
<REPOS> to any CVS commands.

Enabling Watches In The Repository

First, the CVSROOT/notify file must be edited to turn on email
notification. One of the developers can do this, or the repository
administrator can if the developers don't have permission to change the
repository's administrative files. In any case, the first thing to do is
check out the administrative area and edit the notify file:

When you edit the notify file for the first time, you'll see something
like this:

# The "notify" file controls where notifications from watches set by
# "cvs watch add" or "cvs edit" are sent. The first entry on a line is
# a regular expression which is tested against the directory that the
# change is being made to, relative to the $CVSROOT. If it matches,
# then the remainder of the line is a filter program that should contain
# one occurrence of %s for the user to notify, and information on its
# standard input.
#
# "ALL" or "DEFAULT" can be used in place of the regular expression.
#
# For example:
# ALL mail %s -s "CVS notification"

All you really need to do is uncomment the last line by removing the
initial # mark. Although the notify file provides the same
flexible interface as the other administrative files, with regular
expressions matching against directory names, the truth is that you
almost never want to use any of that flexibility. The only reason to
have multiple lines, with each line's regular expression matching a
particular part of the repository, would be if you wanted to use a
different notification method for each project. However, normal email
is a perfectly good notification mechanism, so most projects just use
that.

To specify email notification, the line

ALL mail %s -s "CVS notification"

should work on any standard Unix machine. This command causes
notifications to be sent as emails with the subject line CVS
notification (the special expression ALL matches any directory, as
usual). Having uncommented that line, commit the notify file so the
repository is aware of the change:

Editing the notify file in this way may be all that you'll need to do
for watches in the repository. However, if there are remote developers
working on the project, you may need to edit the CVSROOT/users
file, too. The purpose of the users file is to tell CVS where to send
email notifications for those users who have external email addresses.
The format of each line in the users file is:

The CVS username at the beginning of the line corresponds to a CVS
username in CVSROOT/password (if present and the pserver access
method is being used), or failing that, the server-side system username
of the person running CVS. Following the colon is an external email
address to which CVS should send watch notifications for that user.

Unfortunately, as of this writing, the users file does not exist in the
stock CVS distribution. Because it's an administrative file, you must
not only create, cvs add, and commit it in the usual way, but also add
it to CVSROOT/checkoutlist so that a checked-out copy is always
maintained in the repository.

When in doubt, you should test by running the command line given in the
notify file manually. Just replace the %s in

mail %s -s "CVS notification"

with what you have following the colon in users. If it works when you
run it at a command prompt, it should work in the users file, too.

When it's over, the checkout file will look like this:

# The "checkoutlist" file is used to support additional version controlled
# administrative files in $CVSROOT/CVSROOT, such as template files.
#
# The first entry on a line is a filename which will be checked out from
# the corresponding RCS file in the $CVSROOT/CVSROOT directory.
# The remainder of the line is an error message to use if the file cannot
# be checked out.
#
# File format:
#
# [<whitespace>]<filename><whitespace><error message><end-of-line>
#
# comment lines begin with '#'
users Unable to check out 'users' file in CVSROOT.

The last command, cvs watch add hello.c, tells CVS to notify jrandom if
anyone else starts working on hello.c (that is, it adds jrandom to
hello.c's watch list). For CVS to send notifications as soon as a file
is being edited, the user who is editing it has to announce the fact by
running cvs edit on the file first. CVS has no other way of knowing
when someone starts working on a file. Once checkout is done, CVS isn't
usually invoked until the next update or commit, which happens after the
file has already been edited:

When qsmith runs cvs edit hello.c, CVS looks at the watch list for
hello.c, sees that jrandom is on it, and sends email to jrandom telling
her that qsmith has started editing the file. The email even appears to
come from qsmith:

After receiving these emails, jrandom may want to update hello.c
immediately to see what qsmith has done, or perhaps she'll email qsmith
to find out why he's working on that file. Note that nothing forced
qsmith to remember to run cvs edit - presumably he did it because he
wanted jrandom to know what he was up to (anyway, even if he forgot to
do cvs edit, his commits would still trigger notifications). The reason
to use cvs edit is that it notifies watchers before you start to work on
a file. The watchers can contact you if they think there may be a
conflict, before you've wasted a lot of time.

CVS assumes that anyone who runs cvs edit on a file wants to be added to
the file's watch list, at least temporarily, in case someone else starts
to edit it. When qsmith ran cvs edit, he became a watcher of hello.c.
Both he and jrandom would have received notification if a third party
had run cvs edit on that file (or committed it).

However, CVS also assumes that the person editing the file only wants to
be on its watch list while he or she is editing it. Such users are
taken off the watch list when they're done editing. If they prefer to
be permanent watchers of the file, they would have to run cvs watch add.
CVS makes a default assumption that someone is done editing when he or
she commits a file (until the next time, anyway).

Anyone who gets on a file's watch list solely by virtue of having run
cvs edit on that file is known as a temporary watcher
and is taken off the watch list as soon as she commits a change to the
file. If she wants to edit it again, she has to rerun cvs edit.

CVS's assumption that the first commit ends the editing session is only
a best guess, of course, because CVS doesn't know how many commits the
person will need to finish their changes. The guess is probably
accurate for one-off changes - changes where someone just needs
to make one quick fix to a file and commit it. For more prolonged
editing sessions involving several commits, users should add themselves
permanently to the file's watch list:

Even after the commit, qsmith remains a watcher of hello.c because he
ran watch add on it. (By the way, qsmith will not receive notification
of his own edits; only other watchers will. CVS is smart enough not to
notify you about actions that you took.)

If you answer y, CVS undoes all your changes and notifies
watchers that you're not editing the file anymore. If you answer
n, CVS keeps your changes and also keeps you registered as an
editor of the file (so no notification goes out - in fact, it's as if
you never ran cvs unedit at all). The possibility of CVS
undoing all of your changes at a single keystroke is a bit scary, but
the rationale is easy to understand: If you declare to the world that
you're ending an editing session, then any changes you haven't committed
are probably changes you don't mean to keep. At least, that's the way
CVS sees it. Needless to say, be careful!

Controlling What Actions Are Watched

By default, watchers are notified about three kinds of action: edits,
commits, and unedits. However, if you only want to be notified about,
say, commits, you can restrict notifications by adjusting your watch
with the -a flag (a for action):

floss$ cvs watch add -a commit hello.c

Or if you want to watch edits and commits but don't care about unedits,
you could pass the -a flag twice:

floss$ cvs watch add -a edit -a commit hello.c

Adding a watch with the -a flag will never cause any of your existing
watches to be removed. If you were watching for all three kinds of
actions on hello.c, running

floss$ cvs watch add -a commit hello.c

has no effect - you'll still be a watcher for all three actions. To
remove watches, you should run

floss$ cvs watch remove hello.c

which is similar to add in that, by default, it removes your watches for
all three actions. If you pass -a arguments, it removes only the
watches you specify:

floss$ cvs watch remove -a commit hello.c

This means that you want to stop receiving notifications about commits
but continue to receive notifications about edits and unedits (assuming
you were watching edits and unedits to begin with, that is).

There are two special actions you can pass to the -a flag: all or none.
The former means all actions that are eligible for watching (edits,
commits, and unedits, as of this writing), and the latter means none of
these. Because CVS's default behavior, in the absence of -a, is to
watch all actions, and because watching none is the same as removing
yourself from the watch list entirely, it's hard to imagine a situation
in which it would be useful to specify either of these two special
actions. However, cvs edit also takes the -a option, and in this case,
it can be useful to specify all or none. For example, someone working
on a file very briefly may not want to receive any notifications about
what other people do with the file. Thus, this command

paste$ whoami
qsmith
paste$ cvs edit -a none README.txt

causes watchers of README.txt to be notified that qsmith is about to
work on it, but qsmith would not be added as a temporary watcher of
README.txt during his editing session (which he normally would have
been), because he asked not to watch any actions.

Remember that you can only affect your own watches with the cvs watch
command. You may stop watching a certain file yourself, but that won't
change anyone else's watches.

Finding Out Who Is Watching What

Sometimes you may want to know who's watching before you even run cvs
edit or want to see who is editing what without adding yourself to any
watch lists. Or you may have forgotten exactly what your own status is.
After setting and unsetting a few watches and committing some files,
it's easy to lose track of what you're watching and editing.

Notice that the last cvs watchers command doesn't specify any files and,
therefore, shows watchers for all files (all those that have watchers,
that is).

All of the watch and edit commands have this behavior in common with
other CVS commands. If you specify file names, they act on those files.
If you specify directory names, they act on everything in that directory
and its subdirectories. If you don't specify anything, they act on the
current directory and everything underneath it, to as many levels of
depth as are available. For example (continuing with the same session):

The last two commands made jrandom a watcher of every file in the
project and then showed the watch list for every file in the project,
respectively. The output of cvs watchers doesn't always line
up perfectly in columns because it mixes tab stops with information of
varying length, but the lines are consistently formatted:

The file hello.c has acquired another watcher: qsmith himself (note that
the file name is not repeated but is left as white space at the
beginning of the line - this would be important if you ever wanted to
write a program that parses watchers output). Because he's editing
hello.c, qsmith has a temporary watch on the file; it goes away as
soon as he commits a new revision of hello.c. The prefix t in
front of each of the actions indicates that these are temporary watches.
If qsmith adds himself as a regular watcher of hello.c as well

he is listed as both a temporary watcher and a permanent watcher. You
may think that the permanent watch status would simply override the
temporary, so that the line would look like this:

qsmith edit unedit commit

However, CVS can't just replace the temporary watches because it doesn't
know in what order things happen. Will qsmith remove himself from the
permanent watch list before ending his editing session, or will he
finish the edits while still remaining a watcher? If the former, the
edit/unedit/commit actions disappear while the tedit/tunedit/tcommit
ones remain; if the latter, the reverse would happen.

Anyway, that side of the watch list is usually not of great concern.
Most of the time, what you want to do is run

floss$ cvs watchers

or

floss$ cvs editors

from the top level of a project and see who's doing what. You don't
really need to know the details of who cares about what actions: the
important things are people and files.

Reminding People To Use Watches

You've probably noticed that the watch features are utterly dependent on
the cooperation of all the developers. If someone just starts editing a
file without first running cvs edit, no one else will know about it
until the changes get committed. Because cvs edit is an additional
step, not part of the normal development routine, people can easily
forget to do it.

Although CVS can't force someone to use cvs edit, it does have a
mechanism for reminding people to do so - the watch on command:

By running cvs watch on hello.c, jrandom causes future checkouts of
myproj to create hello.c read-only in the working copy. When qsmith
tries to work on it, he'll discover that it's read-only and be reminded
to run cvs edit first:

His edit and commit will send notification to all watchers of hello.c.
Note that jrandom isn't necessarily one of them. By running cvs watch
on hello.c, jrandom did not add herself to the watch list for that file;
she merely specified that it should be checked out read-only. People
who want to watch a file must remember to add themselves to its watch
list - CVS cannot help them with that.

Turning on watches for a single file may be the exception. Generally,
it's more common to turn on watches project-wide:

This action amounts to announcing a policy decision for the entire
project: "Please use cvs edit to tell watchers what you're working on,
and feel free to watch any file you're interested in or responsible
for." Every file in the project will be checked out read-only, and thus
people will be reminded that they're expected to use cvs edit before
working on anything.

Curiously, although checkouts of watched files make them read-only,
updates do not. If qsmith had checked out his working copy before
jrandom ran cvs watch on, his files would have stayed read-write,
remaining so even after updates. However, any file he commits after
jrandom turns watching on will become read-only. If jrandom turns off
watches

floss$ cvs watch off

qsmith's read-only files do not magically become read-write. On the
other hand, after he commits one, it will not revert to read-only again
(as it would have if watches were still on).

It's worth noting that qsmith could, were he truly devious, make files
in his working copy writeable by using the standard Unix chmod
command, bypassing cvs edit entirely

paste$ chmod u+w hello.c

or if he wanted to get everything in one fell swoop:

paste$ chmod -R u+w .

There is nothing CVS can do about this. Working copies by their nature
are private sandboxes - the watch features can open them up to public
scrutiny a little bit, but only as far as the developer permits. Only
when a developer does something that affects the repository (such as
commits) is her privacy unconditionally lost.

The relationship among watch add, watch remove, watch on, and watch off
probably seems a bit confusing. It may help to summarize the overall
scheme: add and remove are about adding or removing users
from a file's watch list; they don't have anything to do with whether
files are read-only on checkout or after commits. on and
off are only about file permissions. They don't have anything to
do with who is on a file's watch list; rather, they are tools to help
remind developers of the watch policy by causing working-copy files to
become read-only.

All of this may seem a little inconsistent. In a sense, using watches
works against the grain of CVS. It deviates from the idealized universe
of multiple developers editing freely in their working copies, hidden
from each other until they choose to commit. With watches, CVS gives
developers convenient shortcuts for informing each other of what's going
on in their working copies; however, it has no way to enforce
observation policies, nor does it have a definitive concept of what
constitutes an editing session. Nevertheless, watches can be helpful in
certain circumstances if developers work with them.

What Watches Look Like In The Repository

In the interests of stamping out black boxes and needless mystery, let's
take a quick look at how watches are implemented in the repository.
We'll only take a quick look, though, because it's not pretty.

The fact that fileattr is stored in a CVS subdirectory in the repository
does not mean that the repository has become a working copy. It's
simply that the name CVS was already reserved for bookkeeping in
the working copy, so CVS can be sure no project will ever need a
subdirectory of that name in the repository.

I won't describe the format of fileattr formally; you can
probably grok it pretty well just by watching it change from command to
command:

It should be clear after this brief exposure that the details of parsing
fileattr format are better left to CVS. The main reason to have a basic
understanding of the format - aside from the inherent satisfaction of
knowing what's going on behind the curtain - is if you try to write an
extension to the CVS watch features or debug some problem in them. It's
sufficient to know that you shouldn't be alarmed if you see CVS/
subdirectories popping up in your repository. They're the only safe
place CVS has to store meta-information such as watch lists.

Log Messages And Commit Emails

Commit emails are notices sent out at commit time, showing the log
message and files involved in the commit. They usually go to all
project participants and sometimes to other interested parties. The
details of setting up commit emails were covered in Repository Administration, so I won't repeat them here. I have noticed, however,
that commit emails can sometimes result in unexpected side effects to
projects, effects that you may want to take into account if you set up
commit emails for your project.

First, be prepared for the messages to be mostly ignored. Whether
people read them depends, at least partly, on the frequency of commits
in your project. Do developers tend to commit one big change at the end
of the day, or many small changes throughout the day? The closer your
project is to the latter, the thicker the barrage of tiny commit notices
raining down on the developers all day long, and the less inclined they
will be to pay attention to each message.

This doesn't mean the notices aren't useful, just that you shouldn't
count on every person reading every message. It's still a convenient
way for people to keep tabs on who's doing what (without the
intrusiveness of watches). When the emails go to a publicly
subscribable mailing list, they are a wonderful mechanism for giving
interested users (and future developers!) a chance to see what happens
in the code on a daily basis.

You may want to consider having a designated developer who watches all
log messages and has an overview of activity across the entire project
(of course, a good project leader will probably be doing this anyway).
If there are clear divisions of responsibility - say, certain
developers are "in charge of" certain subdirectories of the project -
you could do some fancy scripting in CVSROOT/loginfo to see that each
responsible party receives specially marked notices of changes made in
their area. This will help ensure that the developers will at least
read the email that pertains to their subdirectories.

A more interesting side effect happens when commit emails aren't
ignored. People start to use them as a realtime communications method.
Here's the kind of log message that can result:

Finished feedback form; fixed the fonts and background colors on the
home page. Whew! Anyone want to go to Mon Lung for lunch?

There's nothing wrong with this, and it makes the logs more fun to read
over later. However, people need to be aware that log messages, such as
the following, are not only distributed by email but is also preserved
forever in the project's history. For example, griping about customer
specifications is a frequent pastime among programmers; it's not hard to
imagine someone committing a log message like this one, knowing that the
other programmers will soon see it in their email:

Truncate four-digit years to two-digits in input. What the customer
wants, the customer gets, no matter how silly & wrong. Sigh.

This makes for an amusing email, but what happens if the customer
reviews the logs someday? (I'll bet similar concerns have led more than
one site to set up CVSROOT/loginfo so that it invokes scripts to guard
against offensive words in log messages!)

The overall effect of commit emails seems to be that people become less
willing to write short or obscure log messages, which is probably a good
thing. However, they may need to be reminded that their audience is
anyone who might ever read the logs, not just the people receiving
commit emails.

Changing A Log Message After Commit

Just in case someone does commit a regrettable log message, CVS enables
you to rewrite logs after they've been committed. It's done with the -m
option to the admin command (this command is covered in more detail
later in this chapter) and allows you to change one log message (per
revision, per file) at a time. Here's how it works:

The original, offensive log message that was committed with revision 1.7
has been replaced with a perfectly innocent - albeit duller - message.
Don't forget the colon separating the revision number from the new log
message.

If the new log message consists of multiple lines, put it in a file and
do this:

floss$ cvs admin -m 1.7:"`cat new-log-message.txt`" date.c

(This example was sent in by Peter Ross <[email protected]>; note
that it only works for Unix users.)

If the bad message was committed into multiple files, you'll have to run
cvs admin separately for each one, because the revision number is
different for each file. Therefore, this is one of the few commands in
CVS that requires you to pass a single file name as argument:

(As is unfortunately often the case with CVS error messages, you have to
see things from CVS's point of view before the message makes sense!)

Invoking admin -m actually changes the project's history, so
use it with care. There will be no record that the log message was ever
changed - it will simply appear as if that revision had been originally
committed with the new log message. No trace of the old message will be
left anywhere (unless you saved the original commit email).

Although its name might seem to imply that only the designated CVS
administrator can use it, in fact anyone can run cvs admin,
as long as they have write access to the project in question.
Nevertheless, it is best used with caution; the ability to change log
messages is mild compared with other potentially damaging things it can
do. See CVS Reference for more about admin, as well as a
way to restrict its use.

Getting Rid Of A Working Copy

In typical CVS usage, the way to get rid of a working copy directory
tree is to remove it like any other directory tree:

paste$ rm -rf myproj

However, if you eliminate your working copy this way, other developers
will not know that you have stopped using it. CVS provides a command to
relinquish a working copy explicitly. Think of release as the opposite
of checkout - you're telling the repository that you're done with the
working copy now. Like checkout, release is invoked from the parent
directory of the tree:

If there are any uncommitted changes in the repository, the release
fails, meaning that it just lists the modified files and otherwise has
no effect. Assuming the tree is clean (totally up to date), release
records in the repository that the working copy has been released.

You can also have release automatically delete the working tree for you,
by passing the -d flag:

As of CVS version 1.10.6, the release command is not able to deduce the
repository's location by examining the working copy (this is because
release is invoked from above the working copy, not within it). You
must pass the -d <REPOS> global option or make sure that your
CVSROOT environment variable is set correctly. (This bug may be fixed
in future versions of CVS.)

The Cederqvist claims that if you use release instead of just deleting
the working tree, people with watches set on the released files will be
notified just as if you had run unedit. However, I tried to
verify this experimentally, and it does not seem to be true.

History - A Summary Of Repository Activity

In Repository Administration, I briefly mentioned the cvs history
command. This command displays a summary of all checkouts, commits,
updates, rtags, and releases done in the repository (at least, since
logging was enabled by the creation of the CVSROOT/history file in the
repository). You can control the format and contents of the summary
with various options.

The first step is to make sure that logging is enabled in your
repository. The repository administrator should first make sure there
is a history file

This history file also needs to be writeable by everyone who uses the
repository, otherwise they'll get an error every time they try to run a
CVS command that modifies that file. The easiest way is simply to make
the file world-writeable:

Before we examine the output, notice that the invocation included two
options: -e and -a. When you run history, you almost always want to
pass options telling it what data to report and how to report it. In
this respect, it differs from most other CVS commands, which usually do
something useful when invoked without any options. In this example, the
two flags meant "everything" (show every kind of event that happened)
and "all" (for all users), respectively.

Another way that history differs from other commands is that, although
it is usually invoked from within a working copy, it does not restrict
its output to that working copy's project. Instead, it shows all
history events from all projects in the repository - the working copy
merely serves to tell CVS from which repository to retrieve the history
data. (In the preceding example, the only history data in that
repository is for the myproj project, so that's all we see.)

The code letters refer to various CVS operations, as shown in Table 6.1.

For operations (such as checkout) that are about the project as a whole
rather than about individual files, the revision and file are omitted,
and the repository path is placed between the equal signs.

Although the output of the history command was designed to be compact,
parseable input for other programs, CVS still gives you a lot of control
over its scope and content. The options shown in Table 6.2 control what
types of events get reported.

Table 6.2 Options to filter by event type.
Option Meaning
========== =========================================================
-m MODULE Show historical events affecting MODULE.
-c Show commit events.
-o Show checkout events.
-T Show tag events.
-x CODE(S) Show all events of type CODE (one or more of OTFWUGCMARE).
-e Show all types of events, period. Once you have
selected what type of events you want reported, you can
filter further with the options shown in Table 6.3.

Table 6.3 Options to filter by user.
Option Meaning
========== =========================================================
-a Show actions taken by all users
-w Show only actions taken from within this working copy
-l Show only the last time this user took the action
-u USER Show records for USER

Annotations - A Detailed View Of Project Activity

The annotate Command

If the history command gives an overview of project activity, the
annotate command is a way of attaching a zoom lens to the view.
With annotate, you can see who was the last person to touch each
line of a file, and at what revision they touched it:

The output of annotate is pretty intuitive. On the left are the
revision number, developer, and date on which the line in question was
added or last modified. On the right is the line itself, as of the
current revision. Because every line is annotated, you can actually see
the entire contents of the file, pushed over to the right by the
annotation information.

If you specify a revision number or tag, the annotations are given as of
that revision, meaning that it shows the most recent modification to
each line at or before that revision. This is probably the most common
way to use annotations - examining a particular revision of a single
file to determine which developers were active in which parts of the
file.

For example, in the output of the previous example, you can see that the
most recent revision of hello.c is 1.21, in which jrandom did something
to the line:

printf ("Hellooo, world!\n");

One way to find out what she did is to diff that revision against the
previous one:

Although the diff reveals the textual facts of the change more
concisely, the annotation may be preferable because it places them in
their historical context by showing how long the previous incarnation of
the line had been present (in this case, all the way since revision
1.1). That knowledge can help you decide whether to look at the logs to
find out the motivation for the change:

Annotations And Branches

By default, annotation always shows activity on the main trunk of
development. Even when invoked from a branch working copy, it shows
annotations for the trunk unless you specify otherwise. (This tendency
to favor the trunk is either a bug or a feature, depending on your point
of view.) You can force CVS to annotate a branch by passing the branch
tag as an argument to -r. Here is an example from a working copy in
which hello.c is on a branch named Brancho_Gratuito, with at
least one change committed on that branch:

Using Keyword Expansion

You may recall a brief mention of keyword expansion in An Overview of CVS. RCS keywords are special words, surrounded by dollar
signs, that CVS looks for in text files and expands into
revision-control information. For example, if a file contains

$Author$

then when updating the file to a given revision, CVS will expand it to
the username of the person who committed that revision:

$Author: jrandom $

CVS is also sensitive to keywords in their expanded form, so that once
expanded, they continue to be updated as appropriate.

Although keywords don't actually offer any information that's not
available by other means, they give people a convenient way to see
revision control facts embedded in the text of the file itself, rather
than by invoking some arcane CVS operation.

The $Log$ keyword is the only one of these that expands to cover
multiple lines, so its behavior is unique. Unlike the others, it does
not replace the old expansion with the new one, but instead inserts the
latest expansion, plus an additional blank line, right after the keyword
(thereby pushing any previous expansions downward). Furthermore, any
text between the beginning of the line and $Log is used as a prefix for
the expansions (this is done to ensure that the log messages stay
commented in program code). For example, if you put this into the file

You may not want to keep your entire log history in the file all the
time; if you do, you can always remove the older sections when it starts
to get too lengthy. It's certainly more convenient than running cvs
log, and it may be worthwhile in projects where people must constantly
read over the logs.

A more common technique may be to include $Revision$ in a file and use
it as the version number for the program. This can work if the project
consists of essentially one file or undergoes frequent releases and has
at least one file that is guaranteed to be modified between every
release. You can even use an RCS keyword as a value in program code:

VERSION = "$Revision: 1.114 $";

CVS expands that keyword just like any other; it has no concept of the
programming language's semantics and does not assume that the double
quotes protect the string in any way.

A complete list of keywords (there are a few more, rather obscure ones)
is given in CVS Reference.

Going Out On A Limb (How To Work With Branches And Survive)

Branches are simultaneously one of the most important and most easily
misused features of CVS. Isolating risky or disruptive changes onto a
separate line of development until they stabilize can be immensely
helpful. If not properly managed, however, branches can quickly propel
a project into confusion and cascading chaos, as people lose track of
what changes have been merged when.

Some Principles For Working With Branches

To work successfully with branches, your development group should adhere
to these principles:

Minimize the number of branches active at any one time. The more
branches under development at the same time, the more likely they are to
conflict when merged into the trunk. In practical terms, the way to
accomplish this is to merge as frequently as you can (whenever a branch
is at a stable point) and to move development back onto the trunk as
soon as feasible. By minimizing the amount of parallel development
going on, everyone is better able to keep track of what's going on on
each branch, and the possibility of conflicts on merge is reduced.

This does not mean minimizing the absolute number of branches in the
project, just the number being worked on at any given time.

Minimize the complexity - that is, the depth - of your branching
scheme. There are circumstances in which it's appropriate to have
branches from branches, but they are very rare (you may get through your
entire programming life without ever encountering one). Just because
CVS makes it technically possible to have arbitrary levels of nested
branching, and to merge from any branch to any other branch, doesn't
mean you actually want to do these things. In most situations, it's
best to have all your branches rooted at the trunk and to merge from
branch to trunk and back out again.

Use consistently named tags to mark all branch and merge events.
Ideally, the meaning of each tag and its relationship to other branches
and tags should be apparent from the tag name. (The point of this will
become clearer as we go through the examples.)

With those principles in mind, let's take a look at a typical branch
development scenario. We'll have jrandom on the trunk and qsmith on the
branch, but note that there could just as well be multiple developers on
the trunk and/or on the branch. Regular development along either line
can involve any number of people; however, the tagging and merging are
best done by one person on each side, as you'll see.

Merging Repeatedly Into The Trunk

Let's assume qsmith needs to do development on a branch for a while, to
avoid destabilizing the trunk that he shares with jrandom. The first
step is to create the branch. Notice how qsmith creates a regular
(non-branch) tag at the branch point first, and then creates the branch:

The point of tagging the trunk first is that it may be necessary someday
to retrieve the trunk as it was the moment the branch was created. If
you ever need to do that, you'll have to have a way of referring to the
trunk snapshot without referring to the branch itself. Obviously, you
can't use the branch tag because that would retrieve the branch, not the
revisions in the trunk that form the root of the branch. The only way
to do it is to make a regular tag at the same revisions the branch
sprouts from. (Some people stick to this rule so faithfully that I
considered listing it as "Branching Principle Number 4: Always create a
non-branch tag at the branch point." However, many sites don't do it,
and they generally seem to do okay, so it's really a matter of taste.)
From here on, I will refer to this non-branch tag as the branch
point tag.

Notice also that a naming convention is being adhered to: The branch
point tag begins with Root-of-, then the actual branch name,
which uses underscores instead of hyphens to separate words. When the
actual branch is created, its tag ends with the suffix -branch so
that you can identify it as a branch tag just by looking at the tag
name. (The branch point tag Root-of-Exotic_Greetings does not
include the -branch because it is not a branch tag.) You don't have to
use this particular naming convention, of course, but you should use
some convention.

Of course, I'm being extra pedantic here. In smallish projects, where
everyone knows who's doing what and confusion is easy to recover from,
these conventions don't have to be used. Whether you use a branch point
tag or have a strict naming convention for your tags depends on the
complexity of the project and the branching scheme. (Also, don't forget
that you can always go back later and update old tags to use new
conventions by retrieving an old tagged version, adding the new tag, and
then deleting the old tag.)

Meanwhile, qsmith needn't wait for the merge to finish before continuing
development, as long as he makes a tag for the batch of changes from
which jrandom merged (later, jrandom will need to know this tag name; in
general, branches depend on frequent and thorough developer
communications):

At this point, qsmith has committed a new change on the branch, and
jrandom has committed a nonconflicting change in a different file on the
trunk. Watch what happens when jrandom tries to merge from the branch
again:

The problem lies in the semantics of merging. Back in An Overview of CVS, I explained that when you run

floss$ cvs update -j BRANCH

in a working copy, CVS merges into the working copy the differences
between BRANCH's root and its tip. The trouble with that behavior, in
this situation, is that most of those changes had already been
incorporated into the trunk the first time that jrandom did a merge.
When CVS tried to merge them in again (over themselves, as it were), it
naturally registered a conflict.

What jrandom really wanted to do was merge into her working copy the
changes between the branch's most recent merge and its current tip. You
can do this by using two -j flags to update, as you may recall from
An Overview of CVS, as long as you know what revision to specify
with each flag. Fortunately, qsmith made a tag at exactly the last
merge point (hurrah for planning ahead!), so this will be no problem.
First, let's have jrandom restore her working copy to a clean state,
from which she can redo the merge:

Even if qsmith had forgotten to tag at the merge point, all hope would
not be lost. If jrandom knew approximately when qsmith's first batch of
changes had been committed, she could try filtering by date:

Although useful as a last resort, filtering by date is less than ideal
because it selects the changes based on people's recollections rather
than dependable developer designations. If qsmith's first mergeable set
of changes had happened over several commits instead of in one commit,
jrandom may mistakenly choose a date or time that would catch some of
the changes, but not all of them.

There's no reason why each taggable point in qsmith's changes needs to
be sent to the repository in a single commit - it just happens to have
worked out that way in these examples. In real life, qsmith may make
several commits between tags. He can work on the branch in isolation,
as he pleases. The point of the tags is to record successive points on
the branch where he considers the changes to be mergeable into the
trunk. As long as jrandom always merges using two -j flags and is
careful to use qsmith's merge tags in the right order and only once
each, the trunk should never experience the double-merge problem.
Conflicts may occur, but they will be the unavoidable kind that requires
human resolution - situations in which both branch and trunk made
changes to the same area of code.

The Dovetail Approach - Merging In And Out Of The Trunk

Merging repeatedly from branch to trunk is good for the people on the
trunk, because they see all of their own changes and all the changes
from the branch. However, the developer on the branch never gets to
incorporate any of the work being done on the trunk.

To allow that, the branch developer needs to add an extra step every now
and then (meaning whenever he feels like merging in recent trunk changes
and dealing with the inevitable conflicts):

paste$ cvs update -j HEAD

The special reserved tag HEAD means the tip of the trunk. The
preceding command merges in all of the trunk changes between the root of
the current branch (Exotic_Greetings-branch) and the current
highest revisions of each file on the trunk. Of course, qsmith should
tag again after doing this, so that the trunk developers can avoid
accidentally merging in their own changes when they're trying to get
qsmith's.

The branch developer can likewise use the trunk's merge tags as
boundaries, allowing the branch to merge exactly those trunk changes
between the last merge and the trunk's current state (the same way the
trunk does merges). For example, supposing jrandom had made some
changes to hello.c after merging from the branch:

Notice that jrandom did not bother to tag after committing the changes
to hello.c, but qsmith did. The principle at work here is that although
you don't need to tag after every little change, you should always tag
after a merge or after committing your line of development up to a
mergeable state. That way, other people - perhaps on other branches -
have a reference point against which to base their own merges.

The Flying Fish Approach - A Simpler Way To Do It

There is a simpler, albeit slightly limiting, variant of the preceding.
In it, the branch developers freeze while the trunk merges, and then the
trunk developers create an entirely new branch, which replaces the old
one. The branch developers move onto that branch and continue working.
The cycle continues until there is no more need for branch development.
It goes something like this (in shorthand - we'll assume [email protected]
has the trunk and [email protected] has the branch, as usual):

floss$ cvs tag -b BRANCH-1
paste$ cvs checkout -r BRANCH-1 myproj

Trunk and branch both start working; eventually, the developers confer
and decide it's time to merge the branch into the trunk:

Now the branch developers switch their working copies over to the new
branch; they know they won't lose any uncommitted changes by doing so,
because they were up-to-date when the merge happened, and the new branch
is coming out of a trunk that has incorporated the changes from the old
branch:

paste$ cvs update -r BRANCH-2

And the cycle continues in that way, indefinitely; just substitute
BRANCH-2 for BRANCH-1 and BRANCH-3 for BRANCH-2.

I call this the Flying Fish technique, because the branch is
constantly emerging from the trunk, traveling a short distance, then
rejoining it. The advantages of this approach are that it's simple (the
trunk always merges in all the changes from a given branch) and the
branch developers never need to resolve conflicts (they're simply handed
a new, clean branch on which to work each time). The disadvantage, of
course, is that the branch people must sit idle while the trunk is
undergoing merge (which can take an arbitrary amount of time, depending
on how many conflicts need to be resolved). Another minor disadvantage
is that it results in many little, unused branches laying around instead
of many unused non-branch tags. However, if having millions of tiny,
obsolete branches doesn't bother you, and you anticipate fairly
trouble-free merges, Flying Fish may be the easiest way to go in terms
of mental bookkeeping.

Whichever way you do it, you should try to keep the separations as short
as possible. If the branch and the trunk go too long without merging,
they could easily begin to suffer not just from textual drift, but
semantic drift as well. Changes that conflict textually are the easiest
ones to resolve. Changes that conflict conceptually, but not textually,
often prove hardest to find and fix. The isolation of a branch, so
freeing to the developers, is dangerous precisely because it shields
each side from the effects of others' changes...for a time. When you
use branches, communication becomes more vital than ever: Everyone needs
to make extra sure to review each others' plans and code to ensure that
they're all staying on the same track.

Branches And Keyword Expansion - Natural Enemies

If your files contain RCS keywords that expand differently on branch and
trunk, you're almost guaranteed to get spurious conflicts on every
merge. Even if nothing else changed, the keywords are overlapping, and
their expansions won't match. For example, if README.txt contains this
on the trunk

There is one thing to be careful of, however: If you use -kk, it
overrides whatever other keyword expansion mode you may have set for
that file. Specifically, this is a problem for binary files, which are
normally -kb (which suppresses all keyword expansion and line-end
conversion). So if you have to merge binary files in from a branch,
don't use -kk. Just deal with the conflicts by hand instead.

Tracking Third-Party Sources (Vendor Branches)

Sometimes a site will make local changes to a piece of software received
from an outside source. If the outside source does not incorporate the
local changes (and there might be many legitimate reasons why it can't),
the site has to maintain its changes in each received upgrade of the
software.

CVS can help with this task, via a feature known as vendor
branches. In fact, vendor branches are the explanation behind the
puzzling (until now) final two arguments to cvs import: the vendor tag
and release tag that I glossed over in An Overview of CVS.

Here's how it works. The initial import is just like any other initial
import of a CVS project (except that you'll want to choose the vendor
tag and release tag with a little care):

A year later, the next version of the software arrives from Them, Inc.,
and you must incorporate your local changes into it. Their changes and
yours overlap slightly. They've added one new file, modified a couple
of files that you didn't touch, but also modified two files that you
modified.

First you must do another import, this time from the new sources.
Almost everything is the same as it was in the initial import - you're
importing to the same project in the repository, and on the same vendor
branch. The only thing different is the release tag:

My goodness - we've never seen CVS try to be so helpful. It's actually
telling us what command to run to merge the changes. And it's almost
right, too! Actually, the command as given works (assuming that you
adjust yesterday to be any time interval that definitely includes the
first import but not the second), but I mildly prefer to do it by
release tag instead:

Notice how the import told us that there were two conflicts, but the
merge only seems to claim one conflict. It seems that CVS's idea of a
conflict is a little different when importing than at other times.
Basically, import reports a conflict if both you and the vendor modified
a file between the last import and this one. However, when it comes
time to merge, update sticks with the usual definition of "conflict" -
overlapping changes. Changes that don't overlap are merged in the usual
way, and the file is simply marked as modified.

A quick diff verifies that only one of the files actually has conflict
markers:

Exporting For Public Distribution

CVS is a good distribution mechanism for developers, but most users will
obtain the software through a downloadable package instead. This
package is generally not a CVS working copy - it's just a source tree
that can be easily configured and compiled on the user's system.

However, CVS does offer a mechanism to help you create that package,
namely the cvs export command. To export a project is
just like checking out a working copy of the project, except that it
checks out the project tree without any CVS administrative
subdirectories. That is to say, you don't get a working copy, you just
get a source tree that knows nothing about where it came from or what
the CVS versions of its files are. Thus, the exported copy is just like
what the public sees after it downloads and unpacks a distribution.
Assuming the project is arranged to be directly compilable from a
working copy (and it certainly should be!), then it will still be
compilable from the exported copy.

The export command works like checkout, except that it
requires a tag name or date. For example, here we tag the project with
a release name, and then export based on that:

Notice how, since the export command is not invoked from within a
working copy, it's necessary to use the global -d option to tell
CVS which repository to use. Also, in this particular example, we
exported into an explicitly named directory (myproj-1.0) instead
of defaulting to the project's name (myproj), since there was a
working copy of that name already present. This situation is not
uncommon.

After the exported copy is created, as in the above example, the
following might be sufficient to complete the release, if the project is
a simple one:

Of course, running all of these commands by hand is rare. More often,
cvs export is called from within some script that handles all
aspects of release and packaging process. Given that there are often
several "test" releases leading up to each public release, it is
desirable that the procedures for creating a releasable package be
highly automated.

The Humble Guru

If you read and understood (and better yet, experimented with)
everything in this chapter, you may rest assured that there are no big
surprises left for you in CVS - at least until someone adds a major new
feature to CVS. Everything you need to know to use CVS on a major
project has been presented.

Before that goes to your head, let me reiterate the suggestion, first
made in Chapter 4, that you subscribe to the [email protected]
mailing list. Despite having the impoverished signal-to-noise ratio
common to most Internet mailing lists, the bits of signal that do come
through are almost always worth the wait. I was subscribed during the
entire time I wrote this chapter (indeed, for all previous chapters as
well), and you would be amazed to know how many important details I
learned about CVS's behavior from reading other people's posts. If
you're going to be using CVS seriously, and especially if you're the CVS
administrator for a group of developers, you can benefit a lot from the
shared knowledge of all the other serious users out there.

Tips And Troubleshooting

I've said in earlier chapters that CVS is not "black box" software.
Black boxes don't let you peek inside; they don't give you internal
access so that you can fix (or break) things. The premise is that the
black box usually doesn't need to be fixed. Most of the time, the
software should work perfectly, so users don't need internal access.
But when black boxes do fail, they tend to fail completely. Any problem
at all is a showstopper, because there aren't many options for repair.

CVS is more like a perfectly transparent box - except without the box.
Its moving parts are exposed directly to the environment, not
hermetically sealed off, and bits of that environment (unexpected file
permissions, interrupted commands, competing processes, whatever) can
sometimes get inside the mechanism and gum up the gears. But even
though CVS does not always work perfectly, it rarely fails completely,
either. It has the advantage of graceful degradation; the degree to
which it doesn't work is usually proportional to the number and severity
of problems in its environment. If you know enough about what CVS is
trying to do - and how it's trying to do it - you'll know what to do
when things go wrong.

Although I can't list all of the problems that you might encounter, I've
included some of the more common ones here. This chapter is divided
into two sections: The first describes those parts of the environment to
which CVS is most sensitive (mainly repository permissions and the
working copy administrative area), and the second describes some of the
most frequently encountered problems and their solutions. By seeing how
to handle these common situations, you will get a feeling for how to
approach any unexpected problem in CVS.

The Usual Suspects

As a CVS administrator (read "field doctor"), you will find that 90
percent of your users' problems are caused by inconsistent working
copies, and the other 90 percent by incorrect repository permissions.
Therefore, before looking at any specific situations, I'll give a quick
overview of the working copy administrative area and review a few
important things about repository permissions.

The Working Copy Administrative Area

You've already seen the basics of working copy structure in An Overview of CVS; in this section, we'll go into a bit more detail.
Most of the details concern the files in the CVS/ administrative
subdirectories. You already know about Entries, Root, and Repository,
but the CVS/ subdirectory can also contain other files, depending on the
circumstances. I'll describe those other files here, partly so they
don't surprise you when you encounter them, and partly so you can fix
them if they ever cause trouble.

CVS/Entries.Log

Sometimes, a file named CVS/Entries.Log will mysteriously appear.
The sole purpose of this file is to temporarily cache minor changes to
CVS/Entries, until some operation significant enough to be worth
rewriting the entire Entries file comes along. CVS has no ability to
edit the Entries file in place; it must read the entire file in and
write it back out to make any change. To avoid this effort, CVS
sometimes records small changes in Entries.Log, until the next time it
needs to rewrite Entries.

The format of Entries.Log is like Entries, except for an extra letter at
the beginning of each line. A means that the line is to be added
to the main Entries file, and R means it is to be removed.

For the most part, you can ignore Entries.Log; it's rare that a human
has to understand the information it contains. However, if you're
reading over an Entries file to debug some problem in a working copy,
you should also examine Entries.Log.

CVS/Entries.Backup

The CVS/Entries.Backup file is where CVS actually writes out a new
Entries file, before renaming it to Entries (similar to the way
it writes to temporary RCS files in the repository and then moves them
to their proper name when they're complete). Because it becomes Entries
when it's complete, you'll rarely see an Entries.Backup file; if you do
see one, it probably means CVS got interrupted in the middle of some
operation.

CVS/Entries.Static

If the CVS/Entries.Static file exists, it means that the entire
directory has not been fetched from the repository. (When CVS knows a
working directory is in an incomplete state, it will not bring
additional files into that directory.)

The Entries.Static file is present during checkouts and updates and
removed immediately when the operation is complete. If you see
Entries.Static, it means that CVS was interrupted, and its presence
prevents CVS from creating any new files in the working copy. (Often,
running cvs update -d solves the problem and removes
Entries.Static.)

The absence of Entries.Static does not necessarily imply that the
working copy contains all of the project's files. Whenever a new
directory is created in the project's repository, and someone updates
their working copy without passing the -d flag to update, the new
directory will not be created in the working copy. Locally, CVS is
unaware that there is a new directory in the repository, so it goes
ahead and removes the Entries.Static file when the update is complete,
even though the new directory is not present in the working copy.

CVS/Tag

If the CVS/Tag file is present, it names a tag associated, in some
sense, with the directory. I say "in some sense" because, as you know,
CVS does not actually keep any revision history for directories and,
strictly speaking, cannot attach tags to them. Tags are attached to
regular files only or, more accurately, to particular revisions in
regular files.

However, if every file in a directory is on a particular tag, CVS likes
to think of the entire directory as being on the tag, too. For example,
if you were to check out a working copy on a particular branch:

floss$ cvs co -r Bugfix_Branch_1

and then add a file inside it, you'd want the new file's initial
revision to be on that branch, too. For similar reasons, CVS also needs
to know if the directory has a nonbranch sticky tag or date set on it.

Tag files contain one line. The first character on the line is a
single-letter code telling what kind of tag it is, and the rest of the
line is the tag's name. Currently, CVS uses only these three
single-letter codes:

T - A branch tag

N - A nonbranch (regular) tag

D - A sticky date, which occurs if a command such as

floss$ cvs checkout -D 1999-05-15 myproj

or

floss$ cvs update -D 1999-05-15 myproj

is run.

(If you see some other single-letter code, it just means that CVS has
added a new tag type since this chapter was written.)

You should not remove the Tag file manually; instead, use cvs update -A.

Rarities

There are a few other files you may occasionally find in a CVS/ subdirectory:

CVS/Checkin.prog, CVS/Update.prog

CVS/Notify, CVS/Notify.tmp

CVS/Base/, CVS/Baserev, CVS/Baserev.tmp

CVS/Template

These files are usually not the cause of problems, so I'm just listing
them (see CVS Reference for their full descriptions).

Portability And Future Extension

As features are added to CVS, new files (not listed here) may appear in
working copy administrative areas. As new files are added, they'll
probably be documented in the Cederqvist manual, in the node
Working Directory Storage. You can also start looking in
src/cvs.h in the source distribution, if you prefer to learn from code.

Finally, note that all CVS/* files - present and future - use whatever
line-ending convention is appropriate for the working copy's local
system (for example, LF for Unix or CRLF for Windows). This means that
if you transport a working copy from one kind of machine to the other,
CVS won't be able to handle it (but then, you'd have other problems,
because the revision-controlled files themselves would have the wrong
line-end conventions for their new location).

Repository Permissions

CVS does not require any particular repository permission scheme - it
can handle a wide variety of permission arrangements. However, to avoid
getting confusing behaviors, you should make sure your repository setup
meets at least the following criteria:

If a user wants any kind of access at all - even read-only access - to
a given subdirectory of the repository, she usually needs file
system-level write permission to that subdirectory. This is necessary
because CVS creates temporary lock files in the repository to ensure
data consistency. Even read-only operations (such as checkout or
update) create locks, to signal that they need the data to stay in one
state until they're done.

As noted in Repository Administration, you can get around this
writeability requirement by setting the LockDir parameter in
CVSROOT/config, like this:

LockDir=/usr/local/cvslocks

Of course, then you would need to make sure the directory
/usr/local/cvslocks is writeable by all CVS users. Either way, most CVS
operations, including read-only ones, are going to require a writeable
directory somewhere. By default, that directory is the project's
repository; if you're very security conscious, you can change it to be
somewhere else.

Make sure the CVSROOT/history file is world-writeable (if it exists at
all). If the history file exists, most CVS operations attempt to append
a record to it; if the attempt fails, the operation exits with an error.

Unfortunately (and inexplicably), the history file is not born
world-writeable when you create a new repository with cvs init. At
least with the current version of CVS, you should explicitly change its
permissions after you create a new repository (or just remove it, if you
want to disable history logging entirely).

(This problem may go away - I just now submitted a patch to the CVS
maintainers that makes the history file world-writeable when you
initialize a new repository. So perhaps if you get a more recent
version of CVS than the one available now (September 1999), it won't be
a problem for you.)

For security purposes, you almost certainly want to make sure that most
CVS users do not have Unix-level write access to the CVSROOT directory
in the repository. If someone has checkin access to CVSROOT, they can
edit commitinfo, loginfo, or any of the other trigger files to invoke a
program of their choice - they could even commit a new program if the
one they want isn't on the system already. Therefore, you should assume
that anyone who has commit access to CVSROOT is able to run arbitrary
commands on the system.

General Troubleshooting Tips

The bulk of this chapter is organized into a series of questions and
answers, similar to an Internet FAQ (Frequently Asked Questions)
document. These are all based on actual CVS experiences. But before we
look at individual cases, let's take a moment to consider CVS
troubleshooting from a more general point of view.

The first step in solving a CVS problem is usually to determine whether
it's a working copy or repository problem. The best technique for doing
that, not surprisingly, is to see if the problem occurs in working
copies other than the one where it was first noticed. If it does, it's
likely a repository issue; otherwise, it's probably just a local issue.

Working copy problems tend to be encountered more frequently, not
because working copies are somehow less reliable than repositories, but
because each repository usually has many working copies. Although most
working copy knots can be untied with enough patience, you may
occasionally find it more time-efficient simply to delete the working
copy and check it out again.

Of course, if checking out again takes too long, or there is
considerable uncommitted state in the working copy that you don't want
to lose, or if you just want to know what's wrong, it's worth digging
around to find the cause of the problem. When you start digging around,
one of the first places to look is in the CVS/ subdirectories. Check
the file contents and the file permissions. Very occasionally, the
permissions can mysteriously become read-only or even unreadable. (I
suspect this is caused by users accidentally mistyping Unix commands
rather than any mistake on CVS's part.)

Repository problems are almost always caused by incorrect file and
directory permissions. If you suspect a problem may be due to bad
repository permissions, first find out the effective repository user ID
of the person who's having the trouble. For all local and most remote
users, this is either their regular username or the username they
specified when they checked out their working copy. If they're using
the pserver method with user-aliasing (see the section Anonymous Access in Repository Administration), the effective user ID is
the one on the right in the CVSROOT/passwd file. Failure to discover
this early on can cause you to waste a lot of time debugging the wrong
thing.

Some Real Life Problems (With Solutions)

All of these situations are ones I've encountered in my real-life
adventures as a CVS troubleshooter (plus a few items that are not really
problems, just questions that I've heard asked so often that they may as
well be answered here). The list is meant to be fairly comprehensive,
and it may repeat material you've seen in earlier chapters.

The situations are listed according to how frequently they seem to
arise, with the most common ones first.

CVS says it is waiting for a lock; what does that mean?

it means you're trying to access a subdirectory of the repository that
is locked by some other CVS process at the moment. A process is being
run in that directory so it may not be in a consistent state for other
CVS processes to use.

However, if the wait message persists for a long time, it probably means
that a CVS process failed to clean up after itself, for whatever reason.
It can happen when CVS dies suddenly and unexpectedly, say, due to a
power failure on the repository machine.

The solution is to remove the lock files by hand from the repository
subdirectory in question. Go into that part of the repository and look
for files named #cvs.lock or that begin with #cvs.wfl or
#cvs.rfl. Compare the file's timestamps with the start times of
any currently running CVS processes. If the files could not possibly
have been created by any of those processes, it's safe to delete them.
The waiting CVS processes eventually notice when the lock files are gone
- this should take about 30 seconds - and allow the requested
operation to proceed.

CVS claims a file is failing Up-To-Date check; what do I do?

Don't panic - it just means that the file has changed in the repository
since the last time you checked it out or updated it.

Run cvs update on the file to merge in the changes from the
repository. If the received changes conflict with your local changes,
edit the file to resolve the conflict. Then try your commit again - it
will succeed, barring the possibility that someone committed yet another
revision while you were busy merging the last changes.

The --allow-root=/usr/local/newrepos portion is a security
measure, to make sure that people can't use CVS to get pserver access to
repositories that are not supposed to be served remotely. Any
repository intended to be accessible via pserver must be mentioned in an
--allow-root. You can have as many different --allow-root
options as you need for all of your system's repositories (or anyway, as
many as you want until you bump up against your inetd's argument limit).

The pserver access method is STILL not working

Okay, if the problem is not a missing --allow-root, here are a
few other possibilities:

The user has no entry in the CVSROOT/passwd file, and the CVSROOT/config
file has SystemAuth=no so CVS will not fall back on the system password
file (or SystemAuth=yes, but the system password file has no entry for
this user either).

The user has an entry in the CVSROOT/passwd file, but there is no user
by that name on the system, and the CVSROOT/passwd entry does not map
the user to any valid system username.

The password is wrong (but CVS is usually pretty good about informing
the user of this, so that's probably not the answer).

Everything is set up correctly with the passwd files and in
/etc/inetd.conf, but you forgot an entry like this in /etc/services:

cvspserver 2401/tcp

so inetd is not even listening on that port to pass connections off to
CVS.

My commits seem to happen in pieces instead of atomically

That's because CVS commits happen in pieces, not atomically. :-)

More specifically, CVS operations happen directory by directory. When
you do a commit (or an update, or anything else, for that matter)
spanning multiple directories, CVS locks each corresponding repository
directory in turn while it performs the operation for that directory.

For small- to medium-sized projects, this is rarely a problem - CVS
manages to do its thing in each directory so quickly that you never
notice the nonatomicity. Unfortunately, in large projects, scenarios
like the following can occur (imagine this taking place in a project
with at least two deep, many-filed subdirectories, A and B):

User qsmith starts a commit, involving files from both subdirectories.
CVS commits the files in B first (perhaps because qsmith specified the
directories on the command line in that order).

User jrandom starts a cvs update. The update, for whatever reason,
starts with working copy directory A (CVS makes no guarantees about the
order in which it processes directories or files, if left to its own
devices). Note that there is no locking contention, because qsmith is
not active in A yet.

Then, qsmith's commit finishes B, moves on to A, and finishes A.

Finally, jrandom's update moves on to B and finishes it.

Clearly, when this is all over, jrandom's working copy reflects qsmith's
changes to B but not A. Even though qsmith intended the changes to be
committed as a single unit, it didn't happen that way. Now jrandom's
working copy is in a state that qsmith never anticipated.

The solution, of course, is for jrandom to do another cvs update to
fetch the uncaught changes from qsmith's commit. However, that assumes
that jrandom has some way of finding out in the first place that he only
got part of qsmith's changes.

There's no easy answer to this quandary. You simply have to hope that
the inconsistent state of the working copy will somehow become apparent
(maybe the software won't build, or jrandom and qsmith will have a
conversation that's confusing until they realize what must have
happened).

CVS's failure to provide atomic transaction guarantees is widely
considered a bug. The only reason that locks are not made at the top
level of the repository is that this would result in intolerably
frequent lock contentions for large projects with many developers.
Therefore, CVS has chosen the lesser of two evils, reducing the
contention frequency but allowing the possibility of interleaved reads
and writes. Someday, someone may modify CVS (say, speeding up
repository operations) so that it doesn't have to choose between two
evils; until then, we're stuck with nonatomic actions.

For more information, see the node Concurrency in the Cederqvist
manual.

CVS keeps changing file permissions; why does it do that?

In general, CVS doesn't do a very good job of preserving permissions on
files. When you import a project and then check it out, there is no
guarantee that the file permissions in the new working copy will be the
same as when the project was imported. More likely, the working copy
files will be created with the same standard permissions that you
normally get on newly created files.

However, there is at least one exception. If you want to store
executable shell scripts in the project, you can keep them executable in
all working copies by making the corresponding repository file
executable:

Notice that although the file is executable, it is still read-only, as
all repository files should be (remember that CVS works by making a
temporary copy of the RCS file, doing everything in the copy, and then
replacing the original with the copy when ready).

When you import or add an executable file, CVS preserves the executable
bits, so if the permissions were correct from the start, you have
nothing to worry about. However, if you accidentally add the file
before making it executable, you must go into the repository and
manually set the RCS file to be executable.

The repository permissions always dominate. If the file is
nonexecutable in the repository, but executable in the working copy, the
working copy file will also be nonexecutable after you do an update.
Having your files' permissions silently change can be extremely
frustrating. If this happens, first check the repository and see if you
can solve it by setting the appropriate permissions on the corresponding
RCS files.

A feature called PreservePermissions has recently been added to
CVS that may alleviate some of these problems. However, using this
feature can cause other unexpected results (which is why I'm not
recommending it unconditionally here). Make sure you read the nodes
config and Special Files in the Cederqvist before putting
PreservePermissions=yes in CVSROOT/config.

CVS on Windows complains it cannot find my .cvspass file; why?

For pserver connections, CVS on the client side tries to find the
.cvspass file in your home directory. Windows machines don't have a
natural "home" directory, so CVS consults the environment variable
%HOME%. However, you have to be very careful about how you set
HOME. This will work:

set HOME=C:

This will not:

set HOME=C:\

That extra backslash is enough to confuse CVS, and it will be unable to
open C:\\.cvspass.

So, the quick and permanent solution is to put

set HOME=C:

into your autoexec.bat and reboot. CVS pserver should work fine after
that.

My working copy is on several different branches; help?

You mean different subdirectories of your working copy somehow got on
different branches? You probably ran updates with the -r flag, but from
places other than the top level of the working copy.

No big deal. If you want to return to the trunk, just run this

cvs update -r HEAD

or this

cvs update -A

from the top directory. Or, if you want to put the whole working copy
on one of the branches, do this:

cvs update -r Branch_Name

There's nothing necessarily wrong with having one or two subdirectories
of your working copy on a different branch than the rest of it, if you
need to do some temporary work on that branch just in those locations.
However, it's usually a good idea to switch them back when you're done
- life is much less confusing when your whole working copy is on the
same line of development.

When I do export -d I sometimes miss recent commits

This is due to a clock difference between the repository and local
machines. You can solve it by resetting one or both of the clocks, or
specifying a different date as the argument to -D. It's perfectly
acceptable to specify a date in the future (such as -D tomorrow), if
that's what it takes to compensate for the time difference.

I get an error about val-tags; what should I do?

it means the user CVS is running as does not have permission to write to
the CVSROOT/val-tags file. This file stores valid tag names, to give
CVS a fast way to determine what tags are valid. Unfortunately, CVS
sometimes modifies this file even for operations that are read-only with
respect to the repository, such as checking out a project.

This is a bug in CVS and may be fixed by the time you read this. Until
then, the solution is either to make val-tags world-writeable or,
failing that, to remove it or change its ownership to the user running
the CVS operation. (You'd think just changing the permissions would be
enough, but on several occasions I've had to change the ownership, too.)

I am having problems with sticky tags; how do I get rid of them?

Various CVS operations cause the working copy to have a sticky
tag, meaning a single tag that corresponds to each revision for each
file (in the case of a branch, the sticky tag is applied to any new
files added in the working copy). You get a sticky tagged working area
whenever you check out or update by tag or date, for example:

floss$ cvs update -r Tag_Name

or

floss$ cvs checkout -D '1999-08-16'

If a date or a nonbranch tag name is used, the working copy will be a
frozen snapshot of that moment in the project's history - so naturally
you will not be able to commit any changes from it.

To remove a sticky tag, run update with the -A flag

floss$ cvs update -A

which clears all the sticky tags and updates each file to its most
recent trunk revision.

CVS appears to be saying that there's something wrong with the
CVSROOT/modules file. However, what's really going on is a permission
problem in the repository. The directory I'm trying to check out isn't
readable, or one of its parents isn't readable. In this case, it was a
parent:

I cannot seem to turn off watches

You probably did

floss$ cvs watch remove

on all the files, but forgot to also do:

floss$ cvs watch off

A hint for diagnosing watch problems: Sometimes it can be immensely
clarifying to just go into the repository and examine the CVS/fileattr
files directly. See Repository Administration for more
information about them.

CVS is not doing line-end conversion correctly

If you're running the CVS client on a non-Unix platform and are not
getting the line-end conventions that you want in some working copy
files, it's usually because they were accidentally added with -kb when
they shouldn't have been. This can be fixed in the repository with,
believe it or not, the command:

floss$ cvs admin -kkv FILE

The -kkv means to do normal keyword substitution and implies normal
line-end conversions as well. (Internally, CVS is a bit confused about
the difference between keyword substitution and line-end conversion.
This confusion is reflected in the way the -k options can control both
parameters.)

Unfortunately, that admin command only fixes the file in the repository
- your working copy still thinks the file is binary. You can hand edit
the CVS/Entries line for that file, removing the -kb, but that won't
solve the problem for any other working copies out there.

I need to remove a subdirectory in my project; how do I do it?

Well, you can't exactly remove the subdirectory, but you can remove all
of the files in it (first remove them, then cvs remove them, and then
commit). Once the directory is empty, people can have it automatically
pruned out of their working copies by passing the -P flag to update.

Can I copy .cvspass files or portions of them?

Yes, you can. You can copy .cvspass files from machine to
machine, and you can even copy individual lines from one .cvspass file
to another. For high-latency servers, this may be faster than running
cvs login from each working copy machine.

Remember that if you transport a .cvspass file between two machines with
different line-ending conventions, it probably won't work (of course,
you can probably do the line-end conversion manually without too much
trouble).

I just committed some files with the wrong log message

You don't need to hand-edit anything in the repository to solve this.
Just run admin with the -m flag. Remember to have no space between -m
and its argument, and to quote the replacement log message as you would
a normal one:

floss$ cvs admin -m1.17:'I take back what I said about the customer.' hello.c

When people do updates after that, CVS correctly removes the old files
and brings the new files into the working copies just as though they had
been added to the repository in the usual way (except that they'll be at
unusually high revision numbers for supposedly new files).

How can I get a list of all tags in a project?

Currently, there is no convenient way to do this in CVS. The lack is
sorely felt by all users, and I believe work is under way to make this
feature available. By the time you read this, a cvs tags
command or something similar may be available.

Until then, there are workarounds. You can run cvs log -h and read the
sections of the output following the header symbolic names:. Or,
if you happen to be on the repository machine, you can just look at the
beginnings of some of the RCS files directly in the repository. All of
the tags (branches and nonbranches) are listed in the symbols
field:

How can I get a list of all projects in a repository?

As with getting a list of tags, this is not implemented in the most
current version of CVS, but it's highly likely that it will be
implemented soon. I imagine the command will be called cvs list with a
short form of cvs ls, and it probably will both parse the modules file
and list the repository subdirectories.

In the meantime, examining the CVSROOT/modules file (either directly or
by running cvs checkout -c) is probably your best bet. However, if no
one has explicitly made a module for a particular project, it won't show
up there.

Some commands fail remotely but not locally; how should I debug?

Sometimes there's a problem in the communication between the client and
the server. If so, it's a bug in CVS, but how would you go about
tracking down such a thing?

CVS gives you a way to watch the protocol between the client and server.
Before you run the command on the local (working copy) machine, set the
environment variable CVS_CLIENT_LOG. Here's how in Bourne shell
syntax:

floss$ CVS_CLIENT_LOG=clog; export CVS_CLIENT_LOG

Once that variable is set, CVS will record all communications between
client and server in two files whose names are based on the variable's
value:

The clog.in file contains everything that the client sent into
the server, and clog.out contains everything the server sent back
out to the client. Here are the contents of clog.out, to give you a
sense of what the protocol looks like:

The clog.in file is even more complex, because it has to send revision
numbers and other per-file information to the server.

There isn't space here to document the client/server protocol, but you
can read the cvsclient Info pages that were distributed with CVS
for a complete description. You may be able to figure out a good deal
of it just from reading the raw protocol itself. Although you probably
won't find yourself using client logging until you've eliminated all of
the other possible causes of a problem, it is an invaluable tool for
finding out what's really going on between the client and server.

I do not see my problem covered in this chapter

Email an accurate and complete description of your problem to
[email protected], the CVS discussion list. Its members are
located in many different time zones, and I've usually gotten a response
within an hour or two of sending a question. Please join the list by
sending email to [email protected], so you can help
answer questions, too.

I think I have discovered a bug in CVS; what do I do?

CVS is far from perfect - if you've already tried reading the manual
and posting a question on the mailing list, and you still think you're
looking at a bug, then you probably are.

Send as complete a description of the bug as you can to
[email protected] (you can also subscribe to that list; just use
[email protected] instead). Be sure to include the
version number of CVS (both client and server versions, if applicable),
and a recipe for reproducing the bug.

If you have written a patch to fix the bug, include it and mention on
the subject line of your message that you have a patch. The maintainers
will be very grateful.

(Further details about these procedures are outlined in the node
BUGS in the Cederqvist manual and the file HACKING in the source
distribution.)

How can I keep up with changes to CVS?

The troubleshooting techniques and known bugs described in this chapter
are accurate as of (approximately) CVS Version 1.10.7. Things move fast
in the CVS world, however. While I was writing the last few chapters,
the unofficial mantle of CVS maintainership passed from Cyclic Software
to SourceGear, Inc (http://www.sourcegear.com), which purchased
Cyclic. SourceGear has publicly announced its intention to take an
active role in CVS maintainer-ship and has received Cyclic's approval,
which is more or less enough to make it the "lead maintainer" of CVS as
of right now. (The http://www.cyclic.com address will continue
to work, however, so all of the URLs given previously in this book
should remain valid.)

SourceGear is, at this very moment, busy organizing and cleaning up
various patches that have been floating around, with the intention of
incorporating many of them into CVS. Some of these patches will
probably fix bugs listed previously, and others may afford new
troubleshooting tools to CVS users.

The best way to stay up to date with what's going on is to read the NEWS
file in your CVS distribution, watch the mailing lists, and look for
changes to the Cederqvist manual and the online version of this book
(http://cvsbook.red-bean.com).

CVS Reference

This chapter is a complete reference to CVS commands, repository
administrative files, keyword substitution, run control files, working
copy files, and environment variables - everything in CVS as of CVS
version 1.10.7 (more accurately, as of August 20, 1999).

Commands And Options

This section is a reference to all CVS commands. If you are not already
familiar with the syntactic conventions shared by most CVS commands, you
should probably read the relevant subsections before you look up any
particular command.

Organization And Conventions

This section is organized alphabetically to make it easy for you to look
up a particular command or option. The following conventions are used:

Arguments to commands and options are in all-capitalized letters in the
synopsis that begins each explanation. (Note: in the treeware version
of the book, meta-arguments are italicized as well as capitalized; due
to the limitations of standard terminal fonts, I have omitted the
italicization here.)

Optional items appear between square brackets: [ ]. (This works
out okay because square brackets turn out not used in CVS syntaces.)

If you must choose one from a set, the choices are separated by bars,
like this: x|y|z. (And therefore forward slashes (/)
should be interpreted literally - they do not divide choices in a set.)

Plurals or ellipses indicate multiples, usually separated by whitespace.
For example, FILES means one or more files, but [FILES] means zero or
more files. The entry [&MOD...] means an ampersand followed immediately
by a module name, then whitespace, then maybe another ampersand-module,
and so on, zero or more times. (The ellipsis is used because a plural
would have left it unclear whether the ampersand is needed only the
first time or once for each module.)

When a plural is parenthesized, as in FILE(S), it means that although
technically there can be two or more files, usually there is only one.

REV is often used to stand for a revision argument. This is usually
either a revision number or a tag name. There are very few places in
CVS where you can use one but not the other, and those places are noted
in the text.

General Patterns In CVS Commands

The second set of options is sometimes called command options.
Because there are so many of them, though, I'll just call them "options"
in most places to save space.

Many commands are meant to be run within a working copy and, therefore,
may be invoked without file arguments. These commands default to all of
the files in the current directory and below. So when I refer to the
"file" or "files" in the text, I'm talking about the files on which CVS
is acting. Depending on how you invoked CVS, these files may or may not
have been explicitly mentioned on the command line.

Date Formats

Many options take a date argument. CVS accepts a wide variety of date
formats - too many to list here. When in doubt, stick with the
standard ISO 8601 format:

1999-08-23

This means "23 August 1999" (in fact, "23 August 1999" is a perfectly
valid date specifier too, as long as you remember to enclose it in
double quotes). If you need a time of day as well, you can do this:

"1999-08-23 21:20:30 CDT"

You can even use certain common English constructs, such as "now",
"yesterday", and "12 days ago". In general, you can safely experiment
with date formats; if CVS understands your format at all, it most likely
will understand it in the way you intended. If it doesn't understand,
it will exit with an error immediately.

Global Options

Here are all the global options to CVS.

--allow-root=REPOSITORY

The alphabetically first global option is one that is virtually never
used on the command line. The -allow-root option is used with the
pserver command to allow authenticated access to the named
repository (which is a repository top level, such as
/usr/local/newrepos, not a project subdirectory such as
/usr/local/newrepos/myproj).

This global option is virtually never used on the command line.
Normally, the only place you'd ever use it is in /etc/inetd.conf files
(see Repository Administration), which is also about the only
place the pserver command is used.

Every repository to be accessed via cvs pserver on a given
host needs a corresponding -allow-root option in
/etc/inetd.conf. This is a security device, meant to ensure that
people can't use a CVS pserver to gain access to private repositories.

-a

This authenticates all communications with the server. This option has
no effect unless you're connecting via the GSSAPI server (gserver).
GSSAPI connections are not covered in this book, because they're still
somewhat rarely used (although that may change). (See the nodes
Global Options and GSSAPI Authenticated in the Cederqvist
manual for more information.)

-b (Obsolete)

This option formerly specified the directory where the RCS binaries
could be found. CVS now implements the RCS functions internally, so
this option has no effect (it is kept only for backward compatibility).

-d REPOSITORY

This specifies the repository, which might be an absolute pathname or a
more complex expression involving a connection method, username and
host, and path. If it is an expression specifying a connection method,
the general syntax is:

:ext:[email protected]:/usr/local/newrepos - Connects
using rsh, ssh, or some other external connection program.
If the $CVS_RSH environment variable is unset, this defaults to
rsh; otherwise, it uses the value of that variable.

:server:[email protected]:/usr/local/newrepos - Like
:ext:, but uses CVS's internal implementation of rsh. (This may
not be available on all platforms.)

:fork:[email protected]:/usr/local/newrepos - Connects
to a local repository, but using the client/server network protocol
instead of directly accessing the repository files. This is useful for
testing or debugging remote CVS behaviors from your local machine.

:local:[email protected]:/usr/local/newrepos -
Accesses a local repository directly, as though only the absolute path
to the repository had been given.

-e EDITOR

Invokes EDITOR for your commit message, if the commit message was not
specified on the command line with the -m option. Normally, if you
don't give a message with -m, CVS invokes the editor based on the
$CVSEDITOR, $VISUAL, or $EDITOR environment
variables, which it checks in that order. Failing that, it invokes the
popular Unix editor vi.

If you pass both the -e global option and the -m option to commit, the
-e is ignored in favor of the commit message given on the command line
(that way it's safe to use -e in a .cvsrc file).

-f

This global option suppresses reading of the .cvsrc file.

--help [COMMAND] or -H [COMMAND]

These two options are synonymous. If no COMMAND is specified, a basic
usage message is printed to the standard output. If COMMAND is
specified, a usage message for that command is printed.

--help-options

Prints out a list of all global options to CVS, with brief explanations.

--help-synonyms

Prints out a list of CVS commands and their short forms ("up" for
"update", and so on).

-l

Suppresses logging of this command in the CVSROOT/history file in
the repository. The command is still executed normally, but no record
of it is made in the history file.

-n

Doesn't change any files in the working copy or in the repository. In
other words, the command is executed as a "dry run" - CVS goes through
most of the steps of the command but stops short of actually running it.

This is useful when you want to see what the command would have done had
you actually run it. One common scenario is when you want to see what
files in your working directory have been modified, but not do a full
update (which would bring down changes from the repository). By running
cvs -n update, you can see a summary of what's been done
locally, without changing your working copy.

-q

This tells CVS to be moderately quiet by suppressing the printing of
unimportant informational messages. What is considered "important"
depends on the command. For example, in updates, the messages that CVS
normally prints on entering each subdirectory of the working copy are
suppressed, but the one-line status messages for modified or updated
files are still printed.

-Q

This tells CVS to be very quiet, by suppressing all output except what
is absolutely necessary to complete the command. Commands whose sole
purpose is to produce some output (such as diff or
annotate), of course, still give that output. However, commands
that could have an effect independent of any messages that they may
print (such as update or commit) print nothing.

-r

Causes new working files to be created read-only (the same effect as
setting the $CVSREAD environment variable).

If you pass this option, checkouts and updates make the files in your
working copy read-only (assuming your operating system permits it).
Frankly, I'm not sure why one would ever want to use this option.

-s VARIABLE=VALUE

This sets an internal CVS variable named VARIABLE to
VALUE.

On the repository side, the CVSROOT/*info trigger files can
expand such variables to values that were assigned in the -s option.
For example, if CVSROOT/loginfo contains a line like this

myproj /usr/local/bin/foo.pl ${=FISH}

and someone runs a commit from a myproj working copy like this

floss$ cvs -s FISH=carp commit -m "fixed the bait bug"

the foo.pl script is invoked with carp as an argument.
Note the funky syntax, though: The dollar sign, equal sign, and curly
braces are all necessary - if any of them are missing, the expansion
will not take place (at least not as intended). Variable names may
contain alphanumerics and underscores only. Although it is not required
that they consist entirely of capital letters, most people do seem to
follow that convention.

You can use the -s flag as many times as you like in a single command.
However, if the trigger script refers to variables that aren't set in a
particular invocation of CVS, the command still succeeds, but none of
the variables are expanded, and the user sees a warning. For example,
if loginfo has this

myproj /usr/local/bin/foo.pl ${=FISH} ${=BIRD}

but the same command as before is run

floss$ cvs -s FISH=carp commit -m "fixed the bait bug"

the person running the command sees a warning something like this
(placed last in the output)

loginfo:31: no such user variable ${=BIRD}

and the foo.pl script is invoked with no arguments. But if this
command were run

-T DIR

Stores any temporary files in DIR instead of wherever CVS normally puts
them (specifically, this overrides the value of the $TMPDIR
environment variable, if any exists). DIR should be an absolute path.

This option is useful when you don't have write permission (and,
therefore, CVS doesn't either) to the usual temporary locations.

-t

Traces the execution of a CVS command. This causes CVS to print
messages showing the steps that it's going through to complete a
command. You may find it particularly useful in conjunction with the -n
global option, to preview the effects of an unfamiliar command before
running it for real. It can also be handy when you're trying to
discover why a command failed.

-v or --version

Causes CVS to print out its version and copyright information and then
exit with no error.

-w

Causes new working files to be created read-write (overrides any setting
of the $CVSREAD environment variable). Because files are created
read-write by default anyway, this option is rarely used.

If both -r and -w are passed, -w dominates.

-x

Encrypts all communications with the server. This option has no effect
unless you're connecting via the GSSAPI server (gserver). GSSAPI
connections are not covered in this book, because they're still somewhat
rarely used (although that may change). (See the nodes Global
Options and GSSAPI Authenticated in the Cederqvist manual for
more information.)

-z GZIPLEVEL

Sets the compression level on communications with the server. The
argument GZIPLEVEL must be a number from 1 to 9. Level 1 is
minimal compression (very fast, but doesn't compress much); Level 9 is
highest compression (uses a lot of CPU time, but sure does squeeze the
data). Level 9 is only useful on very slow network connections. Most
people find levels between 3 and 5 to be most beneficial.

add

Synopsis: add [OPTIONS] FILES

Alternate names - ad, new

Requires - Working copy, repository

Changes - Working copy

Adds a new file or files to an existing project. Although the
repository is contacted for confirmation, the file does not actually
appear in it until a subsequent commit is performed. (See also
remove and import.)

Options:

-kKEYWORD_SUBSTITUTION_MODE - Specifies that the file is to be stored
with the given RCS keyword substitution mode. There is no space between
the -k and its argument. (See the section Keyword Substitution (RCS Keywords) later in this chapter for a list of valid modes and
examples.)

-m MESSAGE - Records MESSAGE as the creation message, or description,
for the file. This is different from a per-revision log message - each
file has only one description. Descriptions are optional.

As of version 1.10.7, there is a bug in CVS whereby the description is
lost if you add a file via client/server CVS. The rest of the add
process seems to work fine, however, if that's any comfort.

admin

Synopsis: admin [OPTIONS] [FILES]

Alternate names - adm, rcs

Requires - Working copy, repository

Changes - Repository

This command is an interface to various administrative tasks -
specifically, tasks applicable to individual RCS files in the
repository, such as changing a file's keyword substitution mode or
changing a log message after it's been committed.

Although admin behaves recursively if no files are given as arguments,
you normally will want to name files explicitly. It's very rare for a
single admin command to be meaningful when applied to all files in a
project, or even in a directory. Accordingly, when the following
explanations refer to the "file", they mean the file or (rarely) files
passed as arguments to the admin command.

If there is a system group named cvsadmin on the repository
machine, only members of that group can run admin (with the exception of
the cvs admin -k command, which is always permitted). Thus
you can disallow admin for all users by setting the group to have no
users.

Options:

-AOLDFILE - (Obsolete) Appends the RCS access list of OLDFILE to the
access list of the file that is the argument to admin. CVS ignores RCS
access lists, so this option is useless.

-a USER1 [,USER2...] - (Obsolete) Appends the users in the
comma-separated list to the access list of the file. Like -A, this
option is useless in CVS.

-bREV - Sets the revision of the file's default branch (usually the
trunk) to REV. You won't normally need this option, because you can
usually get the revisions you need via sticky tags, but you may use it
to revert to a vendor's version if you're using vendor branches. There
should be no space between the -b and its argument.

-cCOMMENT_PREFIX - (Obsolete) Sets the comment leader of the file to
COMMENT_PREFIX. The comment leader is not used by CVS or even by recent
versions of RCS; therefore, this option is useless and is included only
for backward-compatibility.

-eUSER1[,USER2...] - (Obsolete) Removes the usernames appearing in the
comma-separated list from the access list of the RCS file. Like -a and
-A, this option is now useless in CVS.

-i or -I - These two are so obsolete I'm not even going to tell you
what they used to do. (See the Cederqvist manual if you're curious.)

-kMODE - Sets the file's default keyword substitution mode to MODE.
This option behaves like the -k option to add, only it gives you a way
to change a file's mode after it's been added. (See the section
Keyword Substitution (RCS Keywords) later in this chapter for
valid modes.) There should be no space between -k and its argument.

-L - Sets locking to strict. (See -l below.)

-l[REV] - Locks the file's revision to REV. If REV is omitted, it
locks the latest revision on the default branch (usually the trunk). If
REV is a branch, it locks the latest revision on that branch.

The intent of this option is to give you a way to do reserved
checkouts, where only one user can be editing the file at a time. I'm
not sure how useful this really is, but if you want to try it, you
should probably do so in conjunction with the rcslock.pl script in the
CVS source distribution's contrib/ directory. See comments in that file
for further information. Among other things, those comments indicate
that the locking must be set to strict. (See -L.) There is no
space between -l and its argument.

-mREV:MESSAGE - Changes the log message for revision REV to MESSAGE.
Very handy - along with -k, this is probably the most frequently used
admin option. There are no spaces between option and arguments or
around the colon between the two arguments. Of course, MESSAGE may
contain spaces within itself (in which case, remember to surround it
with quotes so the shell knows it's all one thing).

-NNAME[:[REV]] - Just like -n, except it forces the override of any
existing assignment of the symbolic name NAME, instead of exiting with
error.

-nNAME[:[REV]] - This is a generic interface to assigning, renaming,
and deleting tags. There is no reason, as far as I can see, to prefer
it to the tag command and the various options available there (-d, -r,
-b, -f, and so on). I recommend using the tag command instead. The
NAME and optional REV can be combined in the following ways:

If only the NAME argument is given, the symbolic name (tag) named NAME
is deleted.

If NAME: is given but no REV, NAME is assigned to the latest revision on
the default branch (usually the trunk).

If NAME:REV is given, NAME is assigned to that revision. REV can be a
symbolic name itself, in which case it is translated to a revision
number first (can be a branch number).

If REV is a branch number and is followed by a period (.), NAME
is attached to the highest revision on that branch. If REV is just $,
NAME is attached to revision numbers found in keyword strings in the
working files.

In all cases where a NAME is assigned, CVS exits with an error if there
is already a tag named NAME in the file (but see -N). There are no
spaces between -n and its arguments.

-oRANGE - Deletes the revisions specified by RANGE (also known as
"outdating", hence the -o). Range can be specified in one of the
following ways:

REV1::REV2 - Collapses all intermediate revisions between REV1 and
REV2, so that the revision history goes directly from REV1 to REV2.
After this, any revisions between the two no longer exist, and there
will be a noncontiguous jump in the revision number sequence.

::REV - Collapses all revisions between the beginning of REV's branch
(which may be the beginning of the trunk) and REV, noninclusively of
course. REV is then the first revision on that line.

REV:: - Collapses all revisions between REV and the end of its branch
(which may be the trunk). REV is then the last revision on that line.

REV - Deletes the revision REV (-o1.8 would be equivalent to
-o1.7::1.9).

REV1:REV2 - Deletes the revisions from REV1 to REV2, inclusive. They
must be on the same branch. After this, you cannot retrieve REV1, REV2,
or any of the revisions in between.

:REV - Deletes revisions from the beginning of the branch (or trunk) to
REV, inclusive. (See the preceding warning.)

REV: - Deletes revisions from REV to the end of its branch (or trunk),
inclusive. (See the preceding warning.)

None of the revisions being deleted may have branches or locks. If any
of the revisions have symbolic names attached, you have to delete them
first with tag -d or admin -n. (Actually, right now CVS only protects
against deleting symbolically named revisions if you're using one of the
:: syntaxes, but the single-colon syntaxes may soon change to this
behavior as well.)

Instead of using this option to undo a bad commit, you should commit a
new revision that undoes the bad change. There are no spaces between -o
and its arguments.

-sSTATE[:REV] - Sets the state attribute of revision REV to STATE. If
REV is omitted, the latest revision on the default branch (usually the
trunk) is used. If REV is a branch tag or number, the latest revision
on that branch is used.

Any string of letters or numbers is acceptable for STATE; some commonly
used states are Exp for experimental, Stab for stable, and Rel for
released. (In fact, CVS sets the state to Exp when a file is created.)
Note that CVS uses the state dead for its own purposes, so don't specify
that one.

States are displayed in cvs log output, and in the $Log and $State RCS
keywords in files. There is no space between -s and its arguments.

-t[DESCFILE] - Replaces the description (creation message) for the file
with the contents of DESCFILE, or reads from standard input if no
DESCFILE is specified.

This useful option, unfortunately, does not currently work in
client/server CVS. In addition, if you try it in client/server and omit
DESCFILE, any existing description for the file is wiped out and
replaced with the empty string. If you need to rewrite a file's
description, either do so using only local CVS on the same machine as
the repository or -t-STRING (see below). There is no space between -t
and its argument. DESCFILE may not begin with a hyphen (-).

-t-STRING - Like -t, except that STRING is taken directly as the new
description. STRING may contain spaces, in which case you should
surround it with quotes. Unlike the other syntax for -t, this works in
client/server as well as locally.

-u[REV] - Unlocks revision REV. (See -l.) If REV is omitted, CVS
unlocks the latest lock held by the caller. If REV is a branch, CVS
unlocks the latest revision on that branch. If someone other than the
owner of a lock breaks the lock, a mail message is sent to the original
locker. The content for this message is solicited on standard input
from the person breaking the lock. There is no space between -u and its
argument.

-VRCS_VERSION_NUMBER - (Obsolete) This used to be a way to tell CVS to
produce RCS files acceptable to previous versions of RCS. Now the RCS
format used by CVS is drifting away from the RCS format used by RCS, so
this option is useless. Specifying it results in an error.

-xSUFFIX - (Obsolete) Theoretically, this gives you a way to specify
the suffix for RCS file names. However, CVS and related tools all
depend on that suffix being the default (,v), so this option does
nothing.

annotate

Synopsis: annotate [OPTIONS] [FILES]

Alternate name - ann

Requires - Working copy, repository

Changes - Nothing

Shows information on who last modified each line of each file and when.
Each line of output corresponds to one line of the file. From left to
right, the line displays the revision number of the last modification of
that line, a parenthetical expression containing the user and date of
the modification, a colon, and the contents of the line in the file.

For example, if a file looks like this

this is a test file
it only has too lines
I mean "two"

the annotations for that file could look like this

1.1 (jrandom 22-Aug-99): this is a test file
1.1 (jrandom 22-Aug-99): it only has too lines
1.2 (jrandom 22-Aug-99): I mean "two"

from which you would know that the first two lines were in the initial
revision, and the last line was added or modified (also by jrandom) in
Revision 1.2.

Options:

-D DATE - Shows the annotations as of the latest revision no later than
DATE.

-f - Forces use of the head revision if the specified tag or date is
not found. You can use this in combination with -D or -r to ensure that
there is some output from the annotate command, even if only to show
Revision 1.1 of the file.

-l - Local. Runs in the current working directory only. Does not
descend into subdirectories.

-R - Recursive. Descends into subdirectories (the default). The point
of the -R option is to override any -l option set in a .cvsrc file.

-r REV - Shows annotations as of revision REV (can be a revision number
or a tag).

checkout

Checks out a module from the repository into a working copy. The
working copy is created if it doesn't exist already and updated if it
does. (See also update.)

Options:

-A - Resets any sticky tags, sticky dates, or sticky -k (RCS keyword
substitution mode) options. This is like the -A option to update and is
probably more often used there than with checkout.

-c - Doesn't check anything out; just prints the CVSROOT/modules file,
sorted, on standard output. This is a good way to get an overview of
what projects are in a repository. However, a project without an entry
in modules does not appear (this situation is quite normal because the
name of the project's top-level directory in the repository functions as
the project's "default" module name).

-D DATE - Checks out the latest revisions no later than DATE. This
option is sticky, so you won't be able to commit from the working copy
without resetting the sticky date. (See -A.) This option also implies
-P, described later.

-d DIR - Creates the working copy in a directory named DIR, instead of
creating a directory with the same name as the checked-out module. If
you check out only a portion of a project and the portion is located
somewhere beneath the project's top level, the locally empty
intermediate directories are omitted. You can use -N to suppress this
directory-collapsing behavior.

-f - Forces checkout of the head revision if the specified tag or date
is not found. Most often used in combination with -D or -r to ensure
that something always gets checked out.

-j REV[:DATE] or -j REV1[:DATE] -j REV2[:DATE] - Joins (merges) two
lines of development. This is just like the -j option to update, where
it is more commonly used. (See update for details.)

-k MODE - Substitutes RCS keywords according to MODE (which can
override the default modes for the files). (See the section Keyword Substitution (RCS Keywords) later in this chapter for valid modes.)
The mode chosen will be sticky - future updates of the working copy
will keep that mode.

-l - Local. Checks out the top-level directory of the project only.
Does not process subdirectories.

-R - Commits changes from subdirectories as well as from the current
directory (the default). This option is used only to counteract the
effect of a -l in .cvsrc.

-r REV - Commits to revision REV, which must be either a branch or a
revision on the trunk that is higher than any existing revision.
Commits to a branch always go on the tip of the branch (extending it);
you cannot commit to a specific revision on a branch. Use of this
option sets the new revision as a sticky tag on the file. This can be
cleared with update -A.

The -r REV option implies -f as well. A new revision is committed even
if there are no changes to commit.

diff

Synopsis: diff [OPTIONS] [FILES]

Alternate names - di, dif

Requires - Working copy, repository

Changes - Nothing

Shows the difference between two revisions (in Unix diff format). When
invoked with no options, CVS diffs the repository base revisions against
the (possibly uncommitted) contents of the working copy. The base
revisions are the latest revisions of this working copy retrieved from
the repository; note that there could be even later revisions in the
repository, if someone else committed changes but this working copy
hasn't been updated yet. (See also rdiff.)

Options:

-D DATE - Diffs against the latest revisions no later than DATE.
Behaves like -r REV, except uses dates rather than revisions. (See -r
for details.)

-l - Local. If no files were specified as arguments, this option diffs
files in the current directory, but does not descend into
subdirectories.

-R - Recursive. This option is the opposite of -l. This is the
default behavior, so the only reason to specify -R is to counteract a -l
in a .cvsrc file.

-r REV or -r REV1 -r REV2 - Diffs against (or between) the specified
revisions. With one -r option, this diffs revision REV against your
working copy of that file (so when multiple files are being diffed, REV
is almost always a tag). With two -r options, it diffs REV1 against
REV2 for each file (and the working copy is, therefore, irrelevant).
The two revisions can be in any order - REV1 does not have to be an
earlier revision than REV2. The output reflects the direction of
change. With no -r options, it shows the difference between the working
file and the revision on which it is based.

Diff Compatibility Options

In addition to the preceding options, cvs diff also shares a number of
options with the GNU version of the standard command-line diff program.
Following is a complete list of these options, along with an explanation
of a few of the most commonly used ones. (See the GNU diff documentation
for the others.)

Following are the GNU diff options most frequently used with cvs diff.

-B - Ignores differences that are merely the insertion or deletion of
blank lines (lines containing nothing but whitespace characters).

-b - Ignores differences in the amount of whitespace. This option
treats all whitespace sequences as being equal and ignores whitespace at
line end. More technically, this option collapses each whitespace
sequence in the input to a single space and removes any trailing
whitespace from each line, before taking the diff. (See also -w.)

-c - Shows output in context diff format, defaulting to three lines of
context per difference (for the sake of the patch program, which
requires at least two lines of context).

-C NUM - context=NUM - Like -c, but with NUM lines of context.

-i - Compares case insensitively. Treats upper- and lowercase versions
of a letter as the same.

-u - Shows output in unified diff format.

-w - Ignores all whitespace differences, even when one side of the
input has whitespace where the other has none. Essentially a stronger
version of -b.

edit

Synopsis: edit [OPTIONS] [FILES]

Alternate names - None

Requires - Working copy, repository

Changes - Permissions in working copy, watchlist in repository

Signals that you are about to begin editing a watched file or files.
Also adds you as a temporary watcher to the file's watch list (you'll be
removed when you do cvs unedit). (See also watch,
watchers, unedit, and editors.)

Options:

-a ACTIONS - Specifies for which actions you want to be a temporary
watcher. ACTIONS should be either edit, unedit, commit, all, or none.
(If you don't use -a, the temporary watch will be for all actions.)

-l - Local. Signals editing for files in the current working directory
only.

-R - Recursive (this is the default). Opposite of b; you would only
need to pass -R to counteract a -l in a .cvsrc file.

gserver

Synopsis: gserver

This is the GSSAPI (Generic Security Services API) server. This command
is not normally run directly by users. Instead, it is started up on the
server side when a user connects from a client with the :gserver:
access method:

history

Synopsis: history [OPTIONS] [FILENAME_SUBSTRING(S)]

Alternate names - hi, his

Requires - Repository, CVSROOT/history

Changes - Nothing

Shows a history of activity in the repository. Specifically, this
option shows records of checkouts, commits, rtags, updates, and
releases. By default, the option shows checkouts (but see the -x
option). This command won't work if there's no CVSROOT/history file in
the repository.

The history command differs from other CVS commands in several ways.
First, it must usually be given options to do anything useful (and some
of those options mean different things for history than they do
elsewhere in CVS). Second, instead of taking full file names as
arguments, it takes one or more substrings to match against file names
(all records matching at least one of those substrings are retrieved).
Third, history's output looks a lot like line noise until you learn to
read it, so I'll explain the output format in a special section, after
the options. (See also log.)

Options:

-a - Shows history for all users (otherwise, defaults to self).

-b STR - Shows data back to record containing string STR in the module
name, file name, or repository path.

-f FILE - Reports the most recent event concerning FILE. You can
specify this option multiple times. This is different from the usual
meaning of -f in CVS commands: "Force to head revision as a last
resort."

-l - Shows the record representing the last (as in "most recent") event
of each project. This is different from the usual meaning of -l in CVS
commands: "Run locally, do not recurse."

-m MODULE - This provides a full report about MODULE (a project name).
You can specify this option multiple times.

-n MODULE - Reports the most recent event about MODULE. For example,
checking out the module is about the module itself, but modifying or
updating a file inside the module is about that file, not about the
module. You can specify this option multiple times. This is different
from the usual meaning of -n in CVS commands: "Don't run a
CVSROOT/modules program."

-o - Shows checkout records (the default).

-p REPOS - Shows data for a particular directory in the repository.
You can specify this option multiple times. The meaning of this option
differs from the usual meaning of -p in CVS commands: "Pipe the data to
standard output instead of a file."

This option appears to be at least partially broken as of summer 1999.

-r REV - Shows records referring to revisions since the revision or tag
named REV appears in individual RCS files. Each RCS file is searched
for the revision or tag.

-T - Reports on all tag events.

-t TAG - Shows records since tag TAG was last added to the history
file. This differs from the -r flag in that it reads only the
CVSROOT/history file, not the RCS files, and is therefore much faster.

-w - Shows records that are associated with the same working directory
from which you are invoking history.

-X HISTORYFILE - Uses HISTORYFILE instead of CVSROOT/history. This
option is mainly for debugging and is not officially supported;
nevertheless, you may find it useful (perhaps for generating
human-readable reports from old history files you've kept around).

-x TYPES - Reports on events specified in TYPES. Each type is
represented by a single letter, from the set TOEFWUCGMAR; any
number of letters can be combined. Here is what they mean:

T - Tag

O - Checkout

E - Export

F - Release

W - Update (newly obsolete file removed from working copy)

U - Update (file was checked out over user file)

C - Update (merge, with conflicts)

G - Update (merge, no conflicts)

M - Commit (file was modified)

A - Commit (file was added)

R - Commit (file was removed)

The default, if no -x option is given, is to show checkouts (like
-x O).

-z ZONE - Displays times in output as for time zone ZONE. ZONE is an
abbreviated time zone name, such as UTC, GMT, BST, CDT, CCT, and so on.
A complete list of time zones is available in the TimezoneTable in the
file lib/getdate.c in the CVS source distribution.

History Output

The output of the history command is a series of lines; each line
represents one "history event" and starts with a single code letter
indicating what type of event it is. For example:

The code letters are the same as for the -x option just described.
Following the code letter is the date of the event (expressed in UTC/GMT
time, unless the -z option is used), followed by the user responsible
for the event.

After the user might be a revision number, tag, or date, but only if
such is appropriate for the event (date or tag will be in square
brackets and formatted as shown in the preceding example). If you
commit a file, it shows the new revision number; if you check out with
-D or -r, the sticky date or tag is shown in square brackets. For a
plain checkout, nothing extra is shown.

Next comes the name of the file in question, or module name if the event
is about a module. If the former, the next two things are the
module/project name and the location of the working copy in the user's
home directory. If the latter, the next two things are the name of the
module's checked-out working copy (between two equal signs), followed by
its location in the user's home directory. (The name of the checked-out
working copy may differ from the module name if the -d flag is used with
checkout.)

import

Synopsis: import [OPTIONS] REPOSITORY VENDOR_TAG RELEASE_TAG(S)

Alternate names - im, imp

Requires - Repository, current directory (the source directory)

Changes - Repository

Imports new sources into the repository, either creating a new project
or creating a new vendor revision on a vendor branch of an existing
project. (See Advanced CVS for a basic explanation of vendor
branches in import, which will help you to understand the following.)

It's normal to use import to add many files or directories at once or to
create a new project. To add single files, you should use add.

Options:

-b BRANCH - Imports to vendor branch BRANCH. (BRANCH is an actual
branch number, not a tag.) This is rarely used but can be helpful if
you get sources for the same project from different vendors. A normal
import command assumes that the sources are to be imported on the
default vendor branch, which is "1.1.1". Because it is the default, you
normally don't bother to specify it with -b:

To import to a vendor branch other than the default, you must specify a
different branch number explicitly:

floss$ cvs import -b 1.1.3 -m "from vendor 2" theirproj THEM2 THEM2-0

The 1.1.3 branch can absorb future imports and be merged like any other
vendor branch. However, you must make sure any future imports that
specify -b 1.1.3 also use the same vendor tag (THEM2).
CVS does not check to make sure that the vendor branch matches the
vendor tag. However, if they mismatch, odd and unpredictable things
will happen.

Vendor branches are odd-numbered, the opposite of regular branches.

-d - Takes the file's modification time as the time of import instead
of using the current time. This does not work with client/server CVS.

-I NAME - Gives file names that should be ignored in the import. You
can use this option multiple times in one import. Wildcard patterns are
supported: *.foo means ignore everything ending in .foo.
(See cvsignore in Repository Administrative Files for
details about wildcards.)

-W SPEC - Specifies filters based on file names that should be in
effect for the import. You can use this option multiple times. (See
cvswrappers in Repository Administrative Files for details
about wrapper specs.)

init

Creates a new repository (that is, a root repository in which many
different projects are stored). You will almost always want to use the
global -d option with this, as in

floss$ cvs -d /usr/local/yet_another_repository init

because even if you have a CVSROOT environment variable set, it's
probably pointing to an existing repository, which would be useless and
possibly dangerous in the context of this command. (See Repository Administration for additional steps that you should take after
initializing a new repository.)

kserver

Synopsis: kserver

This is the Kerberos server. (If you have Kerberos libraries Version 4
or below - Version 5 just uses GSSAPI, see gserver.) This
command is not normally run directly by users but is instead started up
on the server side when a user connects from a client with the
:kserver: access method:

log

Synopsis: log [OPTIONS] [FILES]

Alternate names - lo, rlog

Requires - Working copy, repository

Changes - Nothing

Shows log messages for a project, or for files within a project. The
output of log is not quite in the same style as the output of other CVS
commands, because log is based on an older RCS program (rlog). Its
output format gives a header, containing various pieces of
non-revision-specific information about the file, followed by the log
messages (arranged by revision). Each revision shows not merely the
revision number and log message, but also the author and date of the
change and the number of lines added or deleted. All times are printed
in UTC (GMT), not local time.

Because log output is per file, a single commit involving multiple files
may not immediately appear as a conceptually atomic change. However, if
you read all of the log messages and dates carefully, you may be able to
reconstruct what happened. (For information about a tool that can
reformat multifile log output into a more readable form, see
cvs2cl - Generate GNU-Style ChangeLogs in Third-Party Tools for details.) (See also history.)

Options:

As you read over the following filtering options, it may not be
completely clear how they behave when combined. A precise description
of log's behavior is that it takes the intersection of the revisions
selected by -d, -s, and -w, intersected with the union of those selected
by -b and -r.

-b - Prints log information about the default branch only (usually the
highest branch on the trunk). This is usually done to avoid printing
the log messages for side branches of development.

-dDATES - Prints log information for only those revisions that match
the date or date range given in DATES, a semicolon-separated list.
Dates can be given in any of the usual date formats (see Date Formats earlier in this section) and can be combined into ranges as
follows:

DATE1<DATE2 - Selects revisions created between DATE1 and DATE2. If
DATE1 is after DATE2, use > instead; otherwise, no log messages
are retrieved.

<DATE DATE> - All revisions from DATE or earlier.

>DATE DATE< - All revisions from DATE or later.

DATE - Just selects the most recent single revision from DATE or
earlier.

You may use <= and >= instead of < and > to
indicate an inclusive range (otherwise, ranges are exclusive). Multiple
ranges should be separated with semicolons, for example

floss$ cvs log -d"1999-06-01<1999-07-01;1999-08-01<1999-09-01"

selects log messages for revisions committed in June or August of 1999
(skipping July). There can be no space between -d and its arguments.

-h - Prints only the header information for each file, which includes
the file name, working directory, head revision, default branch, access
list, locks, symbolic names (tags), and the file's default keyword
substitution mode. No log messages are printed.

-l - Local. Runs only on files in the current working directory.

-N - Omits the list of symbolic names (tags) from the header. This can
be helpful when your project has a lot of tags but you're only
interested in seeing the log messages.

-R - Prints the name of the RCS file in the repository.

This is different from the usual meaning of -R: "recursive". There's no
way to override a -l for this command, so don't put log -l in your
.cvsrc.

-rREVS - Shows log information for the revisions specified in REVS, a
comma-separated list. REVS can contain both revision numbers and tags.
Ranges can be specified like this:

REV1:REV2 - Revisions from REV1 to REV2 (they must be on the same
branch).

:REV - Revisions from the start of REV's branch up to and including
REV.

REV: - Revisions from REV to the end of REV's branch.

BRANCH - All revisions on that branch, from root to tip.

BRANCH1:BRANCH2 - A range of branches - all revisions on all the
branches in that range.

BRANCH. - The latest (tip) revision on BRANCH.

Finally, a lone -r, with no argument, means select the latest revision
on the default branch (normally the trunk). There can be no space
between -r and its argument.

If the argument to -r is a list, it is comma-separated, not
semicolon-separated like -d.

-sSTATES - Selects revisions whose state attribute matches one of the
states given in STATES, a comma-separated list. There can be no space
between -s and its argument.

If the argument to -s is a list, it is comma-separated, not semicolon-separated like -d.

-t - Like -h, but also includes the file's description (its creation
message).

-wUSERS - Selects revisions committed by users whose usernames appear
in the comma-separated list USERS. A lone -w with no USERS means to
take the username of the person running cvs log.

login

Synopsis: login

Alternate names - logon, lgn

Requires - Repository

Changes - ~/.cvspass file

Contacts a CVS server and confirms authentication information for a
particular repository. This command does not affect either the working
copy or the repository; it just confirms a password (for use with the
:pserver: access method) with a repository and stores the password for
later use in the .cvspass file in your home directory. Future commands
accessing the same repository with the same username will not require
you to rerun login, because the client-side CVS will just consult the
.cvspass file for the password.

If you use this command, you should specify a repository using the
pserver access method, like this

pserver

Synopsis: pserver

Alternate names - None

Requires - Repository

Changes - Nothing

This is the password-authenticating server. This command is not
normally run directly by users but is started up from
/etc/inetd.conf on the server side when a user connects from a
client with the :pserver: access method. (See also the
login and logout commands, and the file .cvspass in
the Run Control Files section in this chapter. See
Repository Administration for details on setting up a
password-authenticating CVS server.)

rdiff

Synopsis: rdiff [OPTIONS] PROJECTS

Alternate names - patch, pa

Requires - Repository

Changes - Nothing

Like the diff command, except it operates directly in the repository
and, therefore, requires no working copy. This command is meant for
obtaining the differences between one release and another of your
project, in a format suitable as input to the patch program (perhaps so
you can distribute patch files to users who want to upgrade).

The operation of the patch program is beyond the scope of this book.
However, note that if the patch file contains diffs for files in
subdirectories, you may need to use the -p option to patch to get it to
apply the differences correctly. (See the patch documentation for more
about this.) (See also diff.)

Options:

-c - Prints output in context diff format (the default).

-D DATE or -D DATE1 -D DATE2 - With one date, this shows the
differences between the files as of DATE and the head revisions. With
two dates, it shows the differences between the dates.

-f - Forces the use of head revision if no matching revision is found
for the -D or -r flag (otherwise, rdiff would just ignore the file).

-l - Local. Won't descend into subdirectories.

-R - Recursive. Descends into subdirectories (the default). You only
specify this option to counteract a -l in your .cvsrc.

-r REV -r REV1 -r REV2 - With one revision, this shows the differences
between revision REV of the files and the head revisions. With two, it
shows the differences between the revisions.

-s - Displays a summary of differences. This shows which files have
been added, modified, or removed, without showing changes in their
content. The output looks like this:

release

Synopsis: release [OPTIONS] DIRECTORY

Alternate names - re, rel

Requires - Working copy

Changes - Working copy, CVSROOT/history

Cancels a checkout (indicates that a working copy is no longer in use).
Unlike most CVS commands that operate on a working copy, this one is not
invoked from within the working copy but from directly above it (in its
parent directory). You either have to set your CVSROOT environment
variable or use the -d global option, as CVS will not be able to find
out the repository from the working copy.

Using release is never necessary. Because CVS doesn't normally do
locking, you can just remove your working copy.

However, if you have uncommitted changes in your working copy or you
want your cessation of work to be noted in the CVSROOT/history file (see
the history command), you should use release. CVS first checks for any
uncommitted changes; if there are any, it warns you and prompts for
continuation. Once the working copy is actually released, that fact is
recorded in the repository's CVSROOT/history file.

Options:

-d - Deletes the working copy if the release succeeds. Without -d, the
working copy remains on disk after the release.

If you created any new directories inside your working copy but did not
add them to the repository, they are deleted along with the rest of the
working copy, if you specified the -d flag.

remove

Synopsis: remove [OPTIONS] [FILES]

Alternate names - rm, delete

Requires - Working copy

Changes - Working copy

Removes a file from a project. Normally, the file itself is removed
from disk when you invoke this command (but see -f). Although this
command operates recursively by default, it is common to explicitly name
the files being removed. Note the odd implication of the previous
sentence: Usually, you run cvs remove on files that don't exist anymore
in your working copy.

Although the repository is contacted for confirmation, the file is not
actually removed until a subsequent commit is performed. Even then, the
RCS file is not really removed from the repository; if it is removed
from the trunk, it is just moved into an Attic/ subdirectory, where it
is still available to exist on branches. If it is removed from a
branch, its location is not changed, but a new revision with state dead
is added on the branch. (See also add.)

Options:

-f - Force. Deletes the file from disk before removing it from CVS.
This meaning differs from the usual meaning of -f in CVS commands:
"Force to head revision".

-l - Local. Runs only in current working directory.

-R - Recursive. Descends into subdirectories (the default). This
option exists only to counteract a -l in .cvsrc.

rtag

Tags a module directly in the repository (requires no working copy).
You probably need to have your CVSROOT environment variable set or use
the -d global option for this to work. (See also tag.)

Options:

-a - Clears the tag from any removed files, because removed files stay
in the repository for historical purposes but are not considered part of
the live project anymore. Although it's illegal to tag files with a tag
name that's already in use, there should be no interference if the name
is only used in removed files (which, from the current point of view of
the project, don't exist anymore).

-b - Creates a new branch, with branch name TAG.

-D DATE - Tags the latest revisions no later than DATE.

-d - Deletes the tag. No record is made of this change - the tag
simply disappears. CVS does not keep a change history for tags.

-F - Forces reassignment of the tag name, if it happens to exist
already for some other revision in the file.

-f - Forces to head revision if a given tag or date is not found. (See
-r and -D.)

-l - Local. Runs in the current directory only.

-n - Won't execute a tag program from CVSROOT/modules. (See the section
Repository Administrative Files later in this chapter for
details about such programs.)

-R - Recursive. Descends into subdirectories (the default). The -R
option exists only to counteract a -l in .cvsrc.

tag

Synopsis: tag [OPTIONS] TAG [FILES]

Alternate names - ta, freeze

Requires - Working copy, repository

Changes - Repository

Attaches a name to a particular revision or collection of revisions for
a project. Often called "taking a snapshot" of the project. This
command is also used to create branches in CVS. (See the -b option -
see also rtag.)

Options:

-b - Creates a branch named TAG.

-c - Checks that the working copy has no uncommitted changes. If it
does, the command exits with a warning, and no tag is made.

-D DATE - Tags the latest revisions no later than DATE.

-d - Deletes the tag. No record is made of this change; the tag simply
disappears. CVS does not keep a change history for tags.

-F - Forces reassignment of the tag name, if it happens to exist
already for some other revision in the file.

-f - Forces to head revision if a given tag or date is not found. (See
-r and -D.)

-l - Local. Runs in the current directory only.

-R - Recursive. Descends into subdirectories (the default). The -R
option exists only to counteract a -l in .cvsrc.

update

Synopsis: update [OPTIONS] [FILES]

Alternate names - up, upd

Requires - Working copy, repository

Changes - Working copy

Merges changes from the repository into your working copy. As a side
effect, it indicates which files in your working copy are modified (but
if the -Q global option is passed, these indications won't be printed).
(See also checkout.)

Options:

-A - Clears any sticky tags, sticky dates, or sticky RCS keyword
expansion modes. This may result in the contents of files changing, if
the trunk-head revisions are different from the former sticky revisions.
(Think of -A as being like a fresh checkout of the project trunk.)

-C - Clean out any locally changed files and replace them with the
latest versions from the repository. This is not necessarily the same
as reverting the files, since the repository may have changed since the
last update or checkout. Any local modifications are saved in
.#file.rev.

Note: this option was implemented in January 2000; if your CVS was
acquired before then, you'd have to upgrade.

-D DATE - Updates to the most recent revisions no later than DATE.
This option is sticky and implies -P. If the working copy has a sticky
date, commits are not possible.

-d - Retrieves absent directories - that is, directories that exist in
the repository but not yet in the working copy. Such directories may
have been created in the repository after the working copy was checked
out. Without this option, update only operates on the directories
present in the working copy; new files are brought down from the
repository, but new directories are not. (See also -P.)

-f - Forces to head revision if no matching revision is found with the
-D or -r flags.

-I NAME - Like the -I option of import.

-j REV[:DATE] or -j REV1[:DATE] -j REV2[:DATE] - Joins, or merges, two
lines of development. Ignoring the optional DATE arguments for the
moment (we'll get to them later), here's how -j works: If only one -j is
given, it takes all changes from the common ancestor to REV and merges
them into the working copy. The common ancestor is the latest
revision that is ancestral to both the revisions in the working
directory and to REV. If two -j options are given, it merges the
changes from REV1 to REV2 into the working copy.

The special tags HEAD and BASE may be used as arguments to -j; they mean
the most recent revision in the repository, and the revision on which
the current working copy file is based, respectively.

As for the optional DATE arguments, if REV is a branch, it is normally
taken to mean the latest revision on that branch, but you can restrict
it to the latest revision no later than DATE. The date should be
separated from the revision by a colon, with no spaces, for instance:

floss$ cvs update -j ABranch:1999-07-01 -j ABranch:1999-08-01

In this example, different dates on the same branch are used, so the
effect is to take the changes on that branch from July to August and
merge them into the working copy. However, note that there is no
requirement that the branch be the same in both -j options.

-k MODE - Does RCS keyword substitution according to MODE. (See the
section Keyword Substitution (RCS Keywords) later in this
chapter.) The mode remains sticky on the working copy, so it will
affect future updates (but see -A).

-l - Local. Updates the current directory only.

-P - Prunes empty directories. Any CVS-controlled directory that
contains no files at the end of the update are removed from the working
copy. (See also -d.)

-p - Sends file contents to standard output instead of to the files.
Used mainly for reverting to a previous revision without producing
sticky tags in the working copy. For example:

floss$ cvs update -p -r 1.3 README.txt > README.txt

Now README.txt in the working copy has the contents of its past Revision
1.3, just as if you had hand-edited it into that state.

-R - Recursive. Descends into subdirectories to update (the default).
The only reason you'd specify it is to counteract a -l in .cvsrc.

-r REV - Updates (or downdates, or crossdates) to revision REV. When
updating a whole working copy, REV is most often a tag (regular or
branch). However, when updating an individual file, it is just as
likely to be a revision number as a tag.

This option is sticky. If the files are switched to a nonbranch tag or
sticky revision, they cannot be committed until the stickiness is
removed. (See -A.) If REV was a branch tag, however, commits are
possible. They'll simply commit new revisions on that branch.

-WSPEC - Specifies wrapper-style filters to use during the update. You
can use this option multiple times. (See cvswrappers in
Repository Administrative Files in this chapter for details about
wrapper specs.) There is no space between -W and its argument.

watch

Sets a watch on one or more files. Unlike most CVS commands, watch
requires a further subcommand to do something useful. (See also
watchers, edit, editors, and unedit, and
users.)

Subcommands:

on - Declares that the files are being watched. This means that they
are created read-only on checkout, and users should do cvs edit to make
them read-write (and notify any watchers that the file is now being
edited). Turning on a watch does not add you to the watch list for any
files. (See watch add and watch remove for that.)

off - Opposite of watch on. Declares that the files are no longer
being watched.

add - Adds you to the list of watchers for this file. You are notified
when someone commits or runs cvs edit or cvs unedit (but see the -a
option).

remove - Opposite of watch add. Removes you from the list of watchers
for this file.

Options (for use with any watch subcommand). All three options have the
same meanings as for edit:

Keyword Substitution (RCS Keywords)

CVS can perform certain textual substitutions in files, allowing you to
keep some kinds of information automatically up to date in your files.
All of the substitutions are triggered by a certain keyword pattern,
surrounded by dollar signs. For example,

$Revision$

in a file expands to something like

$Revision: 1.5 $

and CVS continues to keep the revision string up to date as new
revisions are committed.

Controlling Keyword Expansion

By default, CVS performs keyword expansion unless you tell it to stop.
You can permanently suppress keyword expansion for a file with the -k
option when you add the file to the project, or you can turn it off
later by invoking admin with -k. The -k option offers several different
modes of keyword control; usually you want mode o or b, for example:

floss$ cvs add -ko chapter-9.sgml

This command added chapter-9.sgml to the project with keyword
expansion turned off. It sets the file's default keyword expansion mode
to o, which means no substitution. (Actually, the "o" stands for
"old", meaning to substitute the string with its old value, which is the
same as substituting it for itself, resulting in no change. I'm sure
this logic made sense to somebody at the time.)

Each file's default keyword mode is stored in the repository. However,
each working copy can also have its own local keyword substitution mode
- accomplished with the -k options to checkout or update. You can also
have a mode in effect for the duration of just one command, with the -k
option to diff.

Here are all the possible modes, presented with the -k option prepended
(as one would type at a command line). Any of these options can be used
as either the default or local keyword substitution mode for a file:

-kkv - Expands to keyword and value. This is the default keyword
expansion mode, so you don't need to set it for new files. You might
use it to change a file from another keyword mode, however.

-kkvl - Like -kkv, but includes the locker's name if the revision is
currently locked. (See the -l option to admin for more on this.)

-kk - Won't expand values in keyword strings, just uses the keyword
name. For example, with this option,

$Revision: 1.5 $

and

$Revision$

would both "expand" (okay, contract) to:

$Revision$

-ko - Reuses the keyword string found in the file (hence "o" for
"old"), as it was in the working file just before the commit.

-kb - Like -ko, but also suppresses interplatform line-end conversions.
The "b" stands for "binary"; it is the mode you should use for binary
files.

-kv - Substitutes the keyword with its value, for example

$Revision$

might become:

1.5

Of course, after that's happened once, future substitutions will not
take place, so this option should be used with care.

List Of Keywords

These are all the dollar-sign-delimited keywords that CVS recognizes.
Following is a list of the keyword, a brief description, and an example
of its expanded form:

$Author$ - Author of the change:

$Author: jrandom $

$Date$ - The date and time of the change, in UTC (GMT):

$Date: 1999/08/23 18:21:13 $

$Header$ - Various pieces of information thought to be useful: full
path to the RCS file in the repository, revision, date (in UTC), author,
state, and locker. (Lockers are rare; although in the following example,
qsmith has a lock.):

$Log$ - The log message of this revision, along with the revision
number, date, and author. Unlike other keywords, the previous
expansions are not replaced. Instead, they are pushed down, so that the
newest expansion appears at the top of an ever-growing stack of $Log$
messages:

Any text preceding the $Log$ keyword on the same line will be
prepended to the downward expansions too; this is so that if you use it
in a comment in a program source file, all of the expansion is
commented, too.

$Locker$ - Name of the person who has a lock on this revision (usually
no one):

Storage And Editing

Generally, the administrative files are kept under revision control just
like any other file in the repository (the exceptions are noted).
However, unlike other files, checked-out copies of the administrative
files are stored in the repository, right next to their corresponding
RCS files in the CVSROOT subdirectory. It is these checked-out
copies which actually govern CVS's behavior.

The normal way to modify the administrative files is to check out a
working copy of the CVSROOT module, make your changes, and commit. CVS
updates the checked-out copies in the repository automatically. (See
checkoutlist.) In an emergency, however, it is also possible to
edit the checked-out copies in the repository directly.

Shared Syntax

In all of the administrative files, a # at the beginning of a line
signifies a comment; that line is ignored by CVS. A backslash preceding
a newline quotes the newline out of existence.

Some of the files (commitinfo, loginfo, taginfo, and rcsinfo) share more
syntactic conventions as well. In these files, on the left of each line
is a regular expression (which is matched against a file or directory
name), and the rest of the line is a program, possibly with arguments,
which is invoked if something is done to a file matching the regular
expression. The program is run with its working directory set to the
top of the repository.

In these files, there are two special regular expressions that may be
used: ALL and DEFAULT. ALL matches any file or directory, whether or
not there is some other match for it, and DEFAULT matches only if
nothing else matched.

Shared Variables

The info files also allow certain variables to be expanded at runtime.
To expand a variable, precede it with a dollar sign (and put it in curly
braces just to be safe). Here are the variables CVS knows about:

${CVSROOT} - The top of the repository.

${RCSBIN} - (Obsolete) Don't use this variable. It is only
applicable in CVS Version 1.9.18 and older. Specifying it now may
result in an error.

${CVSEDITOR} ${VISUAL} ${EDITOR} - These all expand to the editor
that CVS is using for a log message.

User Variables

Users can also set their own variables when they run any CVS
command. (See the -s global option.) These variables can be accessed
in the *info files by preceding them with an equal sign, as in
${=VAR}.

checkoutlist

This contains a list of files for which checked-out copies should be
kept in the repository. Each line gives the file name and an error
message for CVS to print if, for some reason, the file cannot be checked
out in the repository:

FILENAME ERROR_MESSAGE

Because CVS already knows to keep checked-out copies of the existing
administrative files, they do not need to be listed in checkoutlist.
Specifically, the following files never need entries in checkoutlist:
loginfo, rcsinfo, editinfo, verifymsg, commitinfo, taginfo, ignore,
checkoutlist, cvswrappers, notify, modules, readers, writers, and
config.

commitinfo

Specifies programs to run at commit time, based on what's being
committed. Each line consists of a regular expression followed by a
command template:

REGULAR_EXPRESSION PROGRAM [ARGUMENTS]

The PROGRAM is passed additional arguments following any arguments you
may have written into the template. These additional arguments are the
full path to the repository, followed by the name of each file about to
be committed. These files can be examined by PROGRAM; their contents
are the same as those of the working copy files about to be committed.
If PROGRAM exits with nonzero status, the commit fails; otherwise, it
succeeds. (See also Shared Syntax earlier in this chapter.)

config

Controls various global (non-project-specific) repository parameters.
The syntax of each line is

ParameterName=yes|no

except for the LockDir parameter, which takes an absolute pathname as
argument.

The following parameters are supported:

RCSBIN (default: =no) - (Obsolete) This option is silently
accepted for backwards compatibility, but no longer has any effect.

SystemAuth (default: =no) - If yes, CVS pserver
authentication tries the system user database - usually
/etc/passwd - if a username is not found in
CVSROOT/passwd. If no, the user must exist in
CVSROOT/passwd to gain access via the :pserver: method.

PreservePermissions (default: =no) - If yes, CVS tries to
preserve permissions and other special file system information (such as
device numbers and symbolic link targets) for files. You probably don't
want to do this, as it does not necessarily behave as expected. (See the
node Special Files in the Cederqvist manual for details.)

TopLevelAdmin (default: =no) - If yes, checkouts create a
CVS/ subdirectory next to each working copy tree (in the parent
directory of the working copy). This can be useful if you will be
checking out many working copies from the same repository; on the other
hand, setting it here affects everyone who uses this repository.

LockDir (unset by default) - The argument after the equal sign is a
path to a directory in which CVS can create lockfiles. If not set,
lockfiles are created in the repository, in locations corresponding to
each project's RCS files. This means that users of those projects must
have file-system-level write access to those repository directories.

cvsignore

Ignores certain files when doing updates, imports, or releases. By
default, CVS already ignores some kinds of files. (For a full list, see
the -I option to import, earlier in this chapter.) You can add to this
list by putting additional file names or wildcard patterns in the
cvsignore file. Each line gives a file name or pattern, for example:

README.msdos
*.html
blah?.out

This causes CVS to ignore any file named README.msdos, any file
ending in .html, and any file beginning with blah and
ending with .out. (Technically, you can name multiple files or
patterns on each line, separated by whitespace, but it is more readable
to keep them to one per line. The whitespace separation rule does,
unfortunately, mean that there's no way to specify a space in a file
name, except to use wildcards.)

A ! anywhere in the list cancels all previous entries. (See
$CVSIGNORE in the section Environment Variables in
this chapter for a fuller discussion of ignore processing.)

cvswrappers

Specifies certain filtering behaviors based on file name. Each line has
a file-globbing pattern (that is, a file name or file wildcards),
followed by an option indicating the filter type and an argument for the
option.

Options:

-m - Specifies an update method. Possible arguments are MERGE, which
means to merge changes into working files automatically, and COPY, which
means don't try to automerge but present the user with both versions of
the file and let them work it out. MERGE is the default, except for
binary files (those whose keyword substitution mode is -kb). (See the
Keyword Substitution (RCS Keywords) section in this chapter.)
Files marked as binary automatically use the COPY method, so there is no
need to make a -m COPY wrapper for them.

This cvswrappers file says to not attempt merges on files ending in
.blob and suppress keyword substitution for files ending in
.blink. (See also the file .cvswrappers in the
Working Copy Files section in this chapter.)

editinfo

history file

Stores an ever-accumulating history of activity in the repository, for
use by the cvs history command. To disable this feature, simply remove
the history file. If you don't remove the file, you should probably
make it world-writeable to avoid permission problems later.

The contents of this file do not modify CVS's behavior in any way
(except for the output of cvs history, of course).

loginfo

Specifies programs to run on the log message for each commit, based on
what's being committed. Each line consists of a regular expression
followed by a command template:

REGULAR_EXPRESSION PROGRAM [ARGUMENTS]

The PROGRAM is passed the log message on its standard input.

Several special codes are available for use in the arguments: %s
expands to the names of the files being committed, %V expands to
the old revisions from before the commit, and %v expands to the
new revisions after the commit. When there are multiple files involved,
each element of the expansion is separated from the others by
whitespace. For example, in a commit involving two files, %s
might expand into hello.c README.txt, and %v into
1.17 1.12.

You may combine codes inside curly braces, in which case, each unit of
expansion is internally separated by commas and externally separated
from the other units by whitespace. Continuing the previous example,
%{sv} expands into hello.c,1.17 README.txt,1.12.

If any % expansion is done at all, the expansion is prefixed by
the path to the project subdirectory (relative to the top of the
repository). So that last expansion would actually be:

myproj hello.c,1.17 README.txt,1.12

If PROGRAM exits with nonzero status, the commit fails; otherwise, it
succeeds. (See also the Shared Syntax section in this
chapter.)

modules

This maps names to repository directories. The general syntax of each
line is:

MODULE [OPTIONS] [&OTHERMODULE...] [DIR] [FILES]

DIR need not be a top-level project directory - it could be a
subdirectory. If any FILES are specified, the module consists of only
those files from the directory.

An ampersand followed by a module name means to include the expansion of
that module's line in place.

Options:

-a - This is an alias module, meaning it expands literally to
everything after the OPTIONS. In this case, the usual DIR/FILES
behavior is turned off, and everything after the OPTIONS is treated as
other modules or repository directories.

If you use the -a option, you may exclude certain directories from other
modules by putting them after an exclamation point (!). For example

top_proj -a !myproj/a-subdir !myproj/b-subdir myproj

means that checking out top_proj will get all of myproj
except a-subdir and b-subdir.

-d NAME - Names the working directory NAME instead of the module name.

-e PROGRAM - Runs PROGRAM whenever files in this module are exported.

-i PROGRAM - Runs PROGRAM whenever files in this module are committed.
The program is given a single argument - the full pathname in the
repository of the file in question. (See commitinfo,
loginfo, and verifymsg for more sophisticated ways to
run commit-triggered programs.)

-o PROGRAM - Runs PROGRAM whenever files in this module are checked
out. The program is given a single argument, the name of the module.

-s STATUS - Declares a status for the module. When the modules file is
printed (with cvs checkout -s), the modules are sorted by module status
and then by name. This option has no other effects in CVS, so go wild.
You can use it to sort anything - status, person responsible for the
module, or the module's file language, for example.

-t PROGRAM - Runs PROGRAM whenever files in this module are tagged with
cvs rtag. The program is passed two arguments: the name of the module
and the tag name. The program is not used for tag, only for rtag. I
have no idea why this distinction is made. You may find the taginfo
file more useful if you want to run programs at tag time.

-u PROGRAM - Runs PROGRAM whenever a working copy of the module is
updated from its top-level directory. The program is given a single
argument, the full path to the module's repository.

notify

Controls how the notifications for watched files are performed. (You may
want to read up on the watch and edit commands, or see the section
Watches (CVS As Telephone) in Advanced CVS.) Each line is
of the usual form:

REGULAR_EXPRESSION PROGRAM [ARGUMENTS]

A %s in ARGUMENTS is expanded to the name of the user to be
notified, and the rest of the information regarding the notification is
passed to PROGRAM on standard input (usually this information is a brief
message suitable for emailing to the user). (See the section
Shared Syntax earlier in this chapter.)

rcsinfo

Specifies a form that should be filled out for log messages that are
written with an interactive editor. Each line of rcsinfo looks like:

REGULAR_EXPRESSION FILE_CONTAINING_TEMPLATE

This template is brought to remote working copies at checkout time, so
if the template file or rcsinfo file changes after checkout, the remote
copies won't know about it and will continue to use the old template.
(See also the section Shared Syntax in this chapter.)

taginfo

Runs a program at tag time (usually done to check that the tag name
matches some pattern). Each line is of the form:

REGULAR_EXPRESSION PROGRAM

The program is handed a set group of arguments. In order, they are the
tag name, the operation (see below), the repository, and then as many
file name/revision-number pairs as there are files involved in the tag.
The file/revision pairs are separated by whitespace, like the rest of
the arguments.

The operation is one of add, mov, or del
(mov means the -F option to tag was used).

If PROGRAM exits with nonzero status, the tag operation will not
succeed. (See also the section Shared Syntax in this chapter.)

users

Maps usernames to email addresses. Each line looks like:

USERNAME:EMAIL_ADDRESS

This sends watch notifications to EMAIL_ADDRESS instead of to USERNAME
at the repository machine. (All this really does is control the
expansion of %s in the notify file.) If EMAIL_ADDRESS includes
whitespace, make sure to surround it with quotes.

If user aliasing is being used in the passwd file, the username that
will be matched is the CVS username (the one on the left), not the
system username (the one on the right, if any).

val-tags

Caches valid tag names for speedier lookups. You should never need to
edit this file, but you may need to change its permissions, or even
ownership, if people are having trouble retrieving or creating tags.

verifymsg

Used in conjunction with rcsinfo to verify the format of log messages.
Each line is of the form:

REGULAR_EXPRESSION PROGRAM [ARGUMENTS]

The full path to the current log message template (see rcsinfo
earlier in this chapter) is appended after the last argument written in
the verifymsg file. If PROGRAM exits with nonzero status, the commit
fails.

Run Control Files

There are a few files on the client (working copy) side that affect
CVS's behavior. In some cases, they are analogs of repository
administrative files; in other cases, they control behaviors that are
only appropriate for the client side.

.cvsrc

Specifies options that you want to be used automatically with every CVS
command. The format of each line is

COMMAND OPTIONS

where each COMMAND is an unabbreviated CVS command, such as checkout or
update (but not co or up). The OPTIONS are those that you want to
always be in effect when you run that command. Here is a common
.cvsrc line:

update -d -P

To specify global options, simple use cvs as the COMMAND.

.cvsignore

You can have a .cvsignore file in your home directory, which will apply
every time you use CVS. You can also have directory-specific ones in
each project directory of a working copy (these last only apply to the
directory where the .cvsignore is located, and not to its
subdirectories).

.cvspass

Stores passwords for each repository accessed via the pserver method.
Each line is of the form:

REPOSITORY LIGHTLY_SCRAMBLED_PASSWORD

The password is essentially stored in cleartext - a very mild
scrambling is done to prevent accidental compromises (such as the root
user unintentionally looking inside the file). However, this scrambling
will not deter any serious-minded person from gaining the password if
they get access to the file.

The .cvspass file is portable. You can copy it from one machine to
another and have all of your passwords at the new machine, without ever
having run cvs login there. (See also the login and
logout commands.)

.cvswrappers

This is a client side version of the cvswrappers file. (See the
Repository Administrative Files section in this chapter.)
There can be a .cvswrappers file in your home directory and in
each directory of a working copy directory, just as with
.cvsignore.

CVS/Checkin.prog

CVS/Entries

Stores the revisions for the files in this directory. Each line is of
the form:

[CODE_LETTER]/FILE/REVISION/DATE/[KEYWORD_MODE]/[STICKY_OPTION]

If CODE_LETTER is present, it must be D for directory (anything
else is silently ignored by CVS, to allow for future expansion), and the
rest of the items on the line are absent.

This file is always present.

CVS/Entries.Backup

This is just a temp file. If you're writing some program to modify the
Entries file, have it write the new contents to
Entries.backup and then atomically rename it to Entries.

CVS/Entries.Log

This is basically a patch file to be applied to Entries after
Entries has been read (this is an efficiency hack, to avoid
having to rewrite all of Entries for every little change). The
format is the same as Entries, except that there is an additional
mandatory code letter at the front of every line: An A means this
line is to be added to what's in Entries; R means it's to
be removed from what's in Entries. Any other letters should be
silently ignored, to allow for future expansion.

CVS/Entries.Static

If this file exists, it means only part of the directory was fetched
from the repository, and CVS will not create additional files in that
directory. This condition can usually be cleared by using
update -d.

CVS/Notify

Stores notifications that have not yet been sent to the server.

CVS/Notify.tmp

Temp file for Notify. The usual procedure for modifying
Notify is to write out Notify.tmp and then rename it to
Notify.

CVS/Repository

The path to the project-specific subdirectory in the repository. This
may be an absolute path, or it may be relative to the path given in
Root.

This file is always present.

CVS/Root

This is the repository; that is, the value of the $CVSROOT
environment variable or the argument to the -d global option.

This file is always present.

CVS/Tag

If there is a sticky tag or date on this directory, it is recorded in
the first line of the file. The first character is a single letter
indicating the type of tag: T, N, or D, for branch
tag, nonbranch tag, or date respectively. The rest of the line is the
tag or date itself.

CVS/Template

Contains a log message template as specified by the rcsinfo file. (See
Repository Administrative Files earlier in this chapter.) It
is relevant only for remote working copies; working copies on the same
machine as the repository just read rcsinfo directly.

$COMSPEC

$CVS_CLIENT_LOG

Used for debugging the client/server protocol. Set this variable to a
file name before you start using CVS; all traffic to the server will be
logged in filename.in, and everything from the server will be logged in
filename.out.

$CVSEDITOR

$CVSIGNORE

A whitespace-separated list of file names and wildcard patterns that CVS
should ignore. (See also the -I option to the import command.)

This variable is appended last to the ignore list during a command. The
list is built up in this order: CVSROOT/cvsignore, the
.cvsignore file in your home directory, the $CVSIGNORE
variable, any -I command option, and finally the contents of
.cvsignore files in the working copy used as CVS works in each
directory. A ! as the ignore specification at any point
nullifies the entire ignore list built up to that point.

$CVSROOT

This specifies the path to the repository. This is overridden with the
-d global option and by the ambient repository for a given working copy.
The path to the repository may be preceded by an access method,
username, and host, according to the following syntax:

$EDITOR

$HOME %HOMEDRIVE% %HOMEPATH%

Where the .cvsrc, .cvspass, and other such files are found
(under Unix, only $HOME is used). In Windows NT,
%HOMEDRIVE% and %HOMEPATH% might be set for you; in
Windows 95, you may need to set them for yourself.

In Windows 95, you may also need to set %HOME%. Make sure not to
give it a trailing backslash; use set HOME=C: or something
similar.

$PATH

$TEMP $TMP $TMPDIR

Where temporary files go (the server uses TMPDIR; Windows NT uses TMP).
Setting this on the client side will not affect the server. Setting
this on either side will not affect where CVS stores temporary lock
files. (See config in the Repository Administrative Files section in this chapter for more information.)

$VISUAL

Third-Party Tools

Many people have written programs to augment CVS. I call these
third-party tools because they have their own maintainers,
separate from the CVS development team. Most of these programs are not
distributed with CVS, although some are. This chapter covers
third-party tools that I have found useful, but that are not distributed
with CVS.

Although there are some very popular and widely used non-command-line or
non-Unix interfaces to CVS (download sites are listed in Repository Administration), this chapter does not discuss most of them. Their
popularity makes it easy to find out more about them from mailing lists
and newsgroups. One exception to this is the Emacs pcl-cvs interface,
which is very useful, but sometimes tricky to install.

pcl-cvs is one of two Emacs/CVS interfaces. The other is the
native VC (Version Control) interface built into Emacs. I prefer
pcl-cvs because it was written exclusively for CVS and, therefore, works
smoothly with the CVS way of doing things. VC, on the other hand, was
designed to work with several different back-end version control systems
- RCS and SCCS, as well as CVS - and is not really "tuned" for CVS.
For example, VC presents a file-based rather than a directory-based
interface to revision control.

The advantages of pcl-cvs are strong enough that many people choose to
download and install it rather than use VC. Unfortunately, pcl-cvs has
two disadvantages: It can be a bit tricky to install (much of this
section is devoted to overcoming possible installation hurdles), and its
recent releases are a bit unstable.

The latter problem is likely to be temporary, but it does raise the
question of which version to use. Stefan Monnier has just recently
taken over the pcl-cvs maintainership; the latest release, 2.9.6
(available from the first URL in the preceding list), was a bit bumpy
when I tried it. No doubt the problems will be smoothed out soon, but
in the meantime, you might want to use an older version. Because I've
been using Version 1.05 daily for a long time now and it's performed
quite well, I'm going to document that version here. Fortunately, the
installation procedures don't change much from version to version. If
you decide to use pcl-cvs, I suggest that you check Monnier's download
site for a version newer than 2.9.6; if there is one, try it out before
regressing all the way to 1.05.

You'll notice that two URLs are given for Version 1.05. The first is
Per Cederqvist's site, where he still makes available an old archive of
pcl-cvs. However, since I'm not sure how much longer his archive will
stay around, I'm also making the 1.05 distribution available from
ftp.red-bean.com.

Although the rest of these instructions use examples from a Version 1.05
distribution, they should apply to later versions as well.

Installing pcl-cvs

If you don't normally deal with Emacs installation and site-maintenance
issues, the pcl-cvs installation procedure may seem a bit daunting. A
little background on how Emacs works may help.

Most higher-level Emacs features are written in a language called "Emacs
Lisp" (Emacs itself is essentially an interpreter for this language).
People add new features to Emacs by distributing files of Emacs Lisp
code. pcl-cvs is written in this language, and it depends on a
library of useful, generic Emacs Lisp functions called Elib (also
written in part by Per Cederqvist, but distributed separately from
pcl-cvs).

Elib is not included in the regular Emacs distribution (at least not FSF
Emacs; I don't know about XEmacs), so you may have to download and
install it yourself before you can use pcl-cvs. You can get it from
ftp://ftp.lysator.liu.se/pub/emacs/elib-1.0.tar.gz. Installation
instructions are contained within the package.

Once Elib is installed, you're ready to build and install pcl-cvs.
These instructions applies both to Version 1.05 and the 2.x series
(although you should check the NEWS and INSTALL files in newer
distributions to see what's changed).

First, unpack pcl-cvs (I'm using Version 1.05, but it could just as
easily have been 2.9.6)

A Makefile is supplied there. According to the instructions in the
INSTALL file, you're supposed to edit a few paths at the top of the
Makefile and then run:

floss$ make install

If that works, great. However, this sometimes results in an error (the
pcl-cvs code itself is very portable, but its installation procedures
sometimes are not). Do this if you get an error:

floss$ make clean
floss$ make

If all goes well, these commands accomplish a significant part of the
installation by byte-compiling all of the Emacs Lisp files.
(Byte-compiling converts a file of human-readable Emacs Lisp code - an
.el file - into a more compact and efficient representation - an .elc
file. Emacs can load and run an .elc file with better performance than
it can a plain .el file.)

I'll proceed as though the byte-compilation stage has succeeded. If the
byte compilation does not appear to succeed, don't worry: The .elc files
are a luxury, not a necessity. They improve performance slightly, but
you can run pcl-cvs from the raw .el files with no problem.

If the make install failed, the next step is to get the Emacs Lisp
(whether .el or .elc) into a directory where Emacs can load it
automatically. Emacs has a designated directory on the system for
locally installed Lisp. To find this directory - it will have a file
named default.el in it - check the following locations, in this
order:

/usr/share/emacs/site-lisp/

/usr/local/share/emacs/site-lisp/

/usr/lib/emacs/site-lisp/

/usr/local/lib/emacs/site-lisp/

Once you've found your site-lisp directory, copy all of the Lisp files
to it (you may have to be root to do this):

floss# cp -f *.el *.elc /usr/share/emacs/site-lisp/

The last step is to tell Emacs about the entry points to pcl-cvs (the
main one being the function cvs-update), so it will know to load the
pcl-cvs code on demand. Because Emacs always reads the default.el file
when it starts up, that's where you need to list the pcl-cvs entry
points.

Fortunately, pcl-cvs provides the necessary content for default.el.
Simply put the contents of pcl-cvs-startup.el into default.el (or
perhaps into your .emacs, if you're just installing this for yourself)
and restart your Emacs.

You may also want to copy the .info files into your info tree and add
pcl-cvs to the table of contents in the dir file.

Using pcl-cvs

Once installed, pcl-cvs is very easy to use. You just run the function
cvs-update, and pcl-cvs brings up a buffer showing what files in your
working copy have been modified or updated. From there, you can commit,
do diffs, and so on.

Because cvs-update is the main entry point, I suggest that you bind it
to a convenient key sequence before going any further. I have it bound
to Ctrl+c v in my .emacs:

(global-set-key "\C-cv" 'cvs-update)

Otherwise, you can run it by typing M-x cvs-update (also known as
Esc-x cvs-update).

When invoked, cvs-update runs cvs update as if in the directory of the
file in the current buffer - just as if you typed cvs update on the
command line in that directory. Here's an example of what you might see
inside Emacs:

PCL-CVS release 1.05 from CVS release $Name: $.
Copyright (C) 1992, 1993 Per Cederqvist
Pcl-cvs comes with absolutely no warranty; for details consult the manual.
This is free software, and you are welcome to redistribute it under certain
conditions; again, consult the TeXinfo manual for details.
Modified ci README.txt
Modified ci fish.c
---------- End ----

Two files have been locally modified (some versions of pcl-cvs show the
subdirectories where the files are located). The next logical action is
to commit one or both of the files, which is what the ci on each line
means. To commit one of them, go to its line and type c. You are
brought to a log message buffer, where you can type a log message as
long as you want (real log message editing is the major advantage of
pcl-cvs over the command line). Type Ctrl+c Ctrl+c when done to
complete the commit.

If you want to commit multiple files at once, sharing a log message,
first use m to mark the files that you intend to commit. An asterisk
appears next to each file as you mark it:

Now when you type c anywhere, it applies to all (and only) the marked
files. Write the log message and commit them with Ctrl+c Ctrl+c
as before.

You can also type d to run cvs diff on a file (or on marked files)
and f to bring a file into Emacs for editing. Other commands are
available; type Ctrl+h m in the update buffer to see what else you
can do.

Error Handling In pcl-cvs

The pcl-cvs program has historically had an odd way of dealing with
error and informational messages from CVS (although this may be
corrected in the latest versions). When it encounters a message from
CVS that it doesn't know about, it gets hysterical and throws you into a
mail buffer, ready to send a pregenerated bug report to the author of
pcl-cvs. Unfortunately, among the CVS messages that pcl-cvs may not
know about are the ones associated with conflicting merges, which,
although not common, certainly do occur from time to time.

If pcl-cvs suddenly dumps you into a mail buffer, don't panic. Read
over the contents of the buffer carefully - the offending CVS output
should be in there somewhere. If it looks like a merge, you can just
get rid of the mail buffer and rerun cvs-update. It should now succeed,
because CVS won't output any merge messages (because the merge has
already taken place).

(Update: this problem appears to have been fixed in more recent versions
of pcl-cvs, so very probably you can ignore this entire warning.)

The Future Of pcl-cvs

Although I may be giving you the impression that pcl-cvs is barely
maintained and a risky investment, the instability appears to be
temporary. Stefan Monnier is a responsive maintainer (I contacted him
several times during the writing of this chapter, and he always answered
right away; he is already making headway on some of the bugs in Version
2.9.6). Very likely by the time this is published, you will be able to
download Version 2.9.7 or later with confidence.

In fact, I just now got an encouraging email on this topic from Greg
Woods, a former maintainer of pcl-cvs, reprinted here with his
permission:

From: [email protected] (Greg A. Woods)
Subject: Re: pcl-cvs maintenance status, stability of recent "release"s?
To: [email protected]
Date: Sun, 29 Aug 1999 18:59:19 -0400 (EDT)
[...]
I've been using Stefan's releases for some time now, and indeed I have
abandoned my own branch of it.
He's done a lot of really good work on PCL-CVS and except for a few odd
quirks in the 2.9.6 version I'm using daily now it is quite usable (and
is approximately infinitely more usable with modern CVS than the one
that was in the CVS distribution! ;-).
I've added a pcl-cvs.README file to my FTP site to point out that the
files there are indeed quite old (at least in Internet time! ;-) and to
give a pointer to Stefan's FTP site too.
[...]

In a later email, Greg said that the FSF is considering including
pcl-cvs in their next release of Emacs (20.5), which would render most
of the preceding installation advice obsolete. Sigh. It's hard to keep
up with free software, sometimes.

cvsutils - General Utilities For Use With CVS

The suite of small programs called cvsutils generally (although
not always) performs offline operations in the CVS working copy.
Offline operations are those that can be done without contacting the
repository, while still leaving the working copy in a consistent state
for the next time the repository is contacted. Offline behavior can be
extremely handy when your network connection to the repository is slow
or unreliable.

The cvsutils programs are listed below in approximate order of
usefulness (according to my opinion), with the more useful ones coming
first. Coincidentally, this also arranges them by safety. Safety is an
issue because some of these utilities can, in their normal course of
operation, cause you to lose local modifications or files from your
working copy. Therefore, read the descriptions carefully before using
these utilities.

This documentation is accurate as of Version 0.1.4. Be sure to read the
README file in any later versions for more up-to-date information.

cvsu

Danger level: None

Contacts repository: No

This does an offline cvs update by comparing the timestamps of files on
disk with their timestamps recorded in CVS/Entries. You can thus tell
which files have been locally modified and which files are not known to
be under CVS control. Unlike cvs update, cvsu does not bring
down changes from the repository.

Although it can take various options, cvsu is most commonly invoked
without any options:

The left-side codes are like the output of cvs update, except that
D means directory. This example shows that chapter-10.sgml has
been modified locally. What the example doesn't show is that cvsu ran
instantly, whereas a normal cvs update would have required half a minute
or so over my slow modem line. Run

cvsdo

Danger level: Low to none

Contacts repository: No

This can simulate the working copy effects of cvs add and cvs remove,
but without contacting the repository. Of course, you'd still have to
commit the changes to make them take effect in the repository, but at
least the add and remove commands themselves can be sped up this way.
Here's how to use it

cvschroot

Danger level: Low

Contacts repository: No

This deals with a repository move by tweaking the working copy to point
to the new repository. This is useful when a repository is copied en
masse to a new location. When that happens, none of the revisions are
affected, but the CVS/Root (and possibly the CVS/Repository) file of
every working copy must be updated to point to the new location. Using
cvschroot is a lot faster than checking out a new copy. Another
advantage is that it doesn't lose your local changes.

cvsdiscard

Danger level: Medium to high

Contacts repository: Maybe

This is the complement of cvspurge. Instead of removing unknown files
but keeping your local changes, cvsdiscard undoes any local changes
(replacing those files with fresh copies from the repository), but keeps
unknown files.

cvs2cl - Generate GNU-Style ChangeLogs

cvs2cl.pl condenses and reformats the output of cvs log to create a
GNU-style ChangeLog file for your project. ChangeLogs are
chronologically organized documents showing the change history of a
project, with a format designed specifically for human-readability (see
the following examples).

The problem with the cvs log command is that it presents its
output on a per-file basis, with no acknowledgement that the same log
message, appearing at roughly the same time in different files, implies
that those revisions were all part of a single commit. Thus, reading
over log output to get an overview of project development is a hopeless
task - you can really only see the history of one file at a time.

In the ChangeLog produced by cvs2cl.pl, identical log messages are
unified, so that a single commit involving a group of files shows up as
one entry. For example:

The first entry shows that four files were committed at once, with the
log message, "Committing from pcl-cvs 2.9, just for kicks.". (The -r
option was used to show the revision number of each file associated with
that log message.)

Like CVS itself, cvs2cl.pl takes the current directory as an implied
argument but acts on individual files if given file name arguments.
Following are a few of the most commonly used options.

h, --help

Show usage (including a complete list of options).

-r, --revisions

Show revision numbers in output. If used in conjunction with -b,
branches are shown as BRANCHNAME.N, where N is the revision on the
branch.

-t, --tags

Show tags (symbolic names) for revisions that have them.

-b, --branches

Show the branch name for revisions on that branch. (See also -r.)

-g OPTS, --global-opts OPTS

Pass OPTS as global arguments to cvs. Internally, cvs2cl.pl invokes cvs
to get the raw log data; thus, OPTS are passed right after the cvs in
that invocation. For example, to achieve quiet behavior and
compression, you can do this:

floss$ cvs2cl.pl -g "-Q -z3"

-l OPTS, --log-opts OPTS

Similar to -g, except that OPTS are passed as command options instead of
global options. To generate a ChangeLog showing only commits that
happened between July 26 and August 15, you can do this:

floss$ cvs2cl.pl -l "'-d1999-07-26<1999-08-15'"

Notice the double-layered quoting - this is necessary in Unix because
the shell that invokes cvs log (inside cvs2cl.pl) interprets the
< as a shell redirection symbol. Therefore, the quotes have to
be passed as part of the argument, making it necessary to surround the
whole thing with an additional set of quotes.

-d, --distributed

Put an individual ChangeLog in each subdirectory, covering only commits
in that subdirectory (as opposed to building one ChangeLog that covers
the directory where cvs2cl.pl was invoked and all subdirectories
underneath it).

cvsq - Queue CVS Commands For Later Connection

cvsq stands for "cvs queued" and it is a small bash script that wraps
around Cyclic's CVS. It makes working with CVS repository a bit easier
for people connected via dial-up, because it can queue CVS commands and
pass them to "real cvs" later.

For example, you can commit files immediately after editing them, when being
offline, so you don't forget about them:

and all changes will be commited into the repository. If uploading of a
particular file fails, it won't be lost - instead, you'll see error
message and the file will stay in cvsq queue.

You can use cvsq even for commands that make no sense when offline - in
that case, the command is immediately passed to cvs and not queued. For
example, you can call cvsq update and it won't be put into the queue but
executed immediately. In fact, you can start using cvsq as a
replacement for cvs.

cvslock - Lock Repositories For Atomicity

This program locks a CVS repository (either for reading or writing) in
the same way that CVS does, so that CVS will honor the locks. This can
be useful when, for example, you need to make a copy of the whole
repository and want to avoid catching parts of commits or other people's
lockfiles.

The cvslock distribution is packaged extremely well and can be installed
according to the usual GNU procedures. Here's a transcript of an
install session:

Now, cvslock is installed as /usr/local/bin/cvslock. When you invoke
it, you can specify the repository with -d or via the $CVSROOT
environment variable, just as with CVS itself (the following examples
use -d). Its only required argument is the name of the directory to
lock, relative to the top of the repository. That directory and all of
its subdirectories will be locked. In this example, there are no
subdirectories, so only one lockfile is created:

Notice that when I cleared the lock (-u for unlock), I had to
specify -p 27378. That's because cvslock uses Unix process
IDs when creating lockfile names to ensure that its locks are unique.
When you unlock, you have to tell cvslock which lock instance to remove,
even if there's only one instance present. Thus, the -p flag tells
cvslock which previous instance of itself it's cleaning up after (you
can use -p with or without -u, though).

If you're going to be working in the repository for a while, doing
various operations directly in the file system, you can use the -s
option to have cvslock start up a new shell for you. It then consults
the $SHELL environment variable in your current shell to
determine which shell to use:

floss$ cvslock -s -d /usr/local/newrepos myproj

The locks remain present until you exit the shell, at which time they
are automatically removed. You can also use the -c option to execute a
command while the repository is locked. Just as with -s, the locks are
put in place before the command starts and removed when it's finished.
In the following example, we lock the repository just long enough to
display a listing of all of the lockfiles:

The command (the argument to the -c option) is run with the specified
repository directory as its working directory.

By default, cvslock creates read-locks. You can tell it to use
write-locks instead by passing the -W option. (You can pass -R to
specify read-locks, but that's the default anyway.) Always remove any
locks when you're finished, so that other users' CVS processes don't
wait needlessly.

Note that cvslock must be run on the machine where the repository
resides - you cannot specify a remote repository. (For more
information, run man cvslock, which is a manual page
installed when you ran make install.)

Other Packages

Many other third-party packages are available for CVS. Following are
pointers to some of these.

CVSUp (Part Of The FreeBSD Project)

CVSUp is an efficient generic mirroring tool with special built-in
support for mirroring CVS repositories. The FreeBSD operating system
uses it to distribute changes from their master repository, so users can
keep up to date conveniently.

CVSWeb: A Web Interface To CVS Repositories

CVSWeb provides a Web interface to browsing CVS repositories. A more
accurate name might be "RCSWeb", because what it actually does is allow
you to browse revisions directly in a repository, viewing log messages
and diffs. Although I've never found it to be a particularly compelling
interface myself, I have to admit that it is intuitive enough and a lot
of sites use it.

The CVS contrib/ Directory

As mentioned in Repository Administration, a number of third-party
tools are shipped with CVS and are collected in the contrib/ directory.
Although I'm not aware of any formal rule for determining which tools
are distributed with CVS, an effort may be in process to gather most of
the widely used third-party tools and put them in contrib/ so people
know where to find them. Until that happens, the best way to find such
tools is to look in contrib/, look at various CVS Web sites, and ask on
the mailing list.

Writing Your Own Tools

CVS can at times seem like a bewildering collection of improvised
standards. There's RCS format, various output formats (history,
annotate, log, update, and so on), several repository administrative
file formats, working copy administrative file formats, the
client/server protocol, the lockfile protocol.... (Are you numb yet? I
could keep going, you know.)

Fortunately, these standards remain fairly consistent from release to
release - so if you're trying to write a tool to work with CVS, you at
least don't have to worry about hitting a moving target. For every
internal standard, there are usually a few people on the
[email protected] mailing list who know it extremely well
(several of them helped me out during the writing of this book). There
is also the documentation that comes with the CVS distribution
(especially doc/cvs.texinfo, doc/cvsclient.texi, and doc/RCSFILES).
Finally, there is the CVS source code itself, the last word on any
question of implementation or behavior.

With all of this at your disposal, there's no reason to hesitate. If
you can think of some utility that would make your life with CVS easier,
go ahead and write it - chances are other people have been wanting it,
too. Unlike a change to CVS itself, a small, standalone external
utility can get wide distribution very quickly, resulting in quicker
feedback for its author and faster bug fixes for all of the users.

Index

Sorry, the index is still in progress.

Since the online format is searchable anyway, I decided the
incompleteness of the index need not delay the release of the chapters.
I hope to have the index finished reasonably soon. Volunteer indexers
are certainly welcome, too - please email
[email protected] if you're interested.

GNU General Public License

GNU General Public License
Version 2, June 1991
Copyright (C) 1989, 1991 Free Software Foundation, Inc.
59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
Preamble
The licenses for most software are designed to take away your freedom to
share and change it. By contrast, the GNU General Public License is intended
to guarantee your freedom to share and change free software--to make sure
the software is free for all its users. This General Public License applies
to most of the Free Software Foundation's software and to any other program
whose authors commit to using it. (Some other Free Software Foundation
software is covered by the GNU Library General Public License instead.) You
can apply it to your programs, too.
When we speak of free software, we are referring to freedom, not price. Our
General Public Licenses are designed to make sure that you have the freedom
to distribute copies of free software (and charge for this service if you
wish), that you receive source code or can get it if you want it, that you
can change the software or use pieces of it in new free programs; and that
you know you can do these things.
To protect your rights, we need to make restrictions that forbid anyone to
deny you these rights or to ask you to surrender the rights. These
restrictions translate to certain responsibilities for you if you distribute
copies of the software, or if you modify it.
For example, if you distribute copies of such a program, whether gratis or
for a fee, you must give the recipients all the rights that you have. You
must make sure that they, too, receive or can get the source code. And you
must show them these terms so they know their rights.
We protect your rights with two steps: (1) copyright the software, and (2)
offer you this license which gives you legal permission to copy, distribute
and/or modify the software.
Also, for each author's protection and ours, we want to make certain that
everyone understands that there is no warranty for this free software. If
the software is modified by someone else and passed on, we want its
recipients to know that what they have is not the original, so that any
problems introduced by others will not reflect on the original authors'
reputations.
Finally, any free program is threatened constantly by software patents. We
wish to avoid the danger that redistributors of a free program will
individually obtain patent licenses, in effect making the program
proprietary. To prevent this, we have made it clear that any patent must be
licensed for everyone's free use or not licensed at all.
The precise terms and conditions for copying, distribution and modification
follow.
TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
0. This License applies to any program or other work which contains a notice
placed by the copyright holder saying it may be distributed under the terms
of this General Public License. The "Program", below, refers to any such
program or work, and a "work based on the Program" means either the Program
or any derivative work under copyright law: that is to say, a work
containing the Program or a portion of it, either verbatim or with
modifications and/or translated into another language. (Hereinafter,
translation is included without limitation in the term "modification".) Each
licensee is addressed as "you".
Activities other than copying, distribution and modification are not covered
by this License; they are outside its scope. The act of running the Program
is not restricted, and the output from the Program is covered only if its
contents constitute a work based on the Program (independent of having been
made by running the Program). Whether that is true depends on what the
Program does.
1. You may copy and distribute verbatim copies of the Program's source code
as you receive it, in any medium, provided that you conspicuously and
appropriately publish on each copy an appropriate copyright notice and
disclaimer of warranty; keep intact all the notices that refer to this
License and to the absence of any warranty; and give any other recipients of
the Program a copy of this License along with the Program.
You may charge a fee for the physical act of transferring a copy, and you
may at your option offer warranty protection in exchange for a fee.
2. You may modify your copy or copies of the Program or any portion of it,
thus forming a work based on the Program, and copy and distribute such
modifications or work under the terms of Section 1 above, provided that you
also meet all of these conditions:
* a) You must cause the modified files to carry prominent notices stating
that you changed the files and the date of any change.
* b) You must cause any work that you distribute or publish, that in
whole or in part contains or is derived from the Program or any part
thereof, to be licensed as a whole at no charge to all third parties
under the terms of this License.
* c) If the modified program normally reads commands interactively when
run, you must cause it, when started running for such interactive use
in the most ordinary way, to print or display an announcement including
an appropriate copyright notice and a notice that there is no warranty
(or else, saying that you provide a warranty) and that users may
redistribute the program under these conditions, and telling the user
how to view a copy of this License. (Exception: if the Program itself
is interactive but does not normally print such an announcement, your
work based on the Program is not required to print an announcement.)
These requirements apply to the modified work as a whole. If identifiable
sections of that work are not derived from the Program, and can be
reasonably considered independent and separate works in themselves, then
this License, and its terms, do not apply to those sections when you
distribute them as separate works. But when you distribute the same sections
as part of a whole which is a work based on the Program, the distribution of
the whole must be on the terms of this License, whose permissions for other
licensees extend to the entire whole, and thus to each and every part
regardless of who wrote it.
Thus, it is not the intent of this section to claim rights or contest your
rights to work written entirely by you; rather, the intent is to exercise
the right to control the distribution of derivative or collective works
based on the Program.
In addition, mere aggregation of another work not based on the Program with
the Program (or with a work based on the Program) on a volume of a storage
or distribution medium does not bring the other work under the scope of this
License.
3. You may copy and distribute the Program (or a work based on it, under
Section 2) in object code or executable form under the terms of Sections 1
and 2 above provided that you also do one of the following:
* a) Accompany it with the complete corresponding machine-readable source
code, which must be distributed under the terms of Sections 1 and 2
above on a medium customarily used for software interchange; or,
* b) Accompany it with a written offer, valid for at least three years,
to give any third party, for a charge no more than your cost of
physically performing source distribution, a complete machine-readable
copy of the corresponding source code, to be distributed under the
terms of Sections 1 and 2 above on a medium customarily used for
software interchange; or,
* c) Accompany it with the information you received as to the offer to
distribute corresponding source code. (This alternative is allowed only
for noncommercial distribution and only if you received the program in
object code or executable form with such an offer, in accord with
Subsection b above.)
The source code for a work means the preferred form of the work for making
modifications to it. For an executable work, complete source code means all
the source code for all modules it contains, plus any associated interface
definition files, plus the scripts used to control compilation and
installation of the executable. However, as a special exception, the source
code distributed need not include anything that is normally distributed (in
either source or binary form) with the major components (compiler, kernel,
and so on) of the operating system on which the executable runs, unless that
component itself accompanies the executable.
If distribution of executable or object code is made by offering access to
copy from a designated place, then offering equivalent access to copy the
source code from the same place counts as distribution of the source code,
even though third parties are not compelled to copy the source along with
the object code.
4. You may not copy, modify, sublicense, or distribute the Program except as
expressly provided under this License. Any attempt otherwise to copy,
modify, sublicense or distribute the Program is void, and will automatically
terminate your rights under this License. However, parties who have received
copies, or rights, from you under this License will not have their licenses
terminated so long as such parties remain in full compliance.
5. You are not required to accept this License, since you have not signed
it. However, nothing else grants you permission to modify or distribute the
Program or its derivative works. These actions are prohibited by law if you
do not accept this License. Therefore, by modifying or distributing the
Program (or any work based on the Program), you indicate your acceptance of
this License to do so, and all its terms and conditions for copying,
distributing or modifying the Program or works based on it.
6. Each time you redistribute the Program (or any work based on the
Program), the recipient automatically receives a license from the original
licensor to copy, distribute or modify the Program subject to these terms
and conditions. You may not impose any further restrictions on the
recipients' exercise of the rights granted herein. You are not responsible
for enforcing compliance by third parties to this License.
7. If, as a consequence of a court judgment or allegation of patent
infringement or for any other reason (not limited to patent issues),
conditions are imposed on you (whether by court order, agreement or
otherwise) that contradict the conditions of this License, they do not
excuse you from the conditions of this License. If you cannot distribute so
as to satisfy simultaneously your obligations under this License and any
other pertinent obligations, then as a consequence you may not distribute
the Program at all. For example, if a patent license would not permit
royalty-free redistribution of the Program by all those who receive copies
directly or indirectly through you, then the only way you could satisfy both
it and this License would be to refrain entirely from distribution of the
Program.
If any portion of this section is held invalid or unenforceable under any
particular circumstance, the balance of the section is intended to apply and
the section as a whole is intended to apply in other circumstances.
It is not the purpose of this section to induce you to infringe any patents
or other property right claims or to contest validity of any such claims;
this section has the sole purpose of protecting the integrity of the free
software distribution system, which is implemented by public license
practices. Many people have made generous contributions to the wide range of
software distributed through that system in reliance on consistent
application of that system; it is up to the author/donor to decide if he or
she is willing to distribute software through any other system and a
licensee cannot impose that choice.
This section is intended to make thoroughly clear what is believed to be a
consequence of the rest of this License.
8. If the distribution and/or use of the Program is restricted in certain
countries either by patents or by copyrighted interfaces, the original
copyright holder who places the Program under this License may add an
explicit geographical distribution limitation excluding those countries, so
that distribution is permitted only in or among countries not thus excluded.
In such case, this License incorporates the limitation as if written in the
body of this License.
9. The Free Software Foundation may publish revised and/or new versions of
the General Public License from time to time. Such new versions will be
similar in spirit to the present version, but may differ in detail to
address new problems or concerns.
Each version is given a distinguishing version number. If the Program
specifies a version number of this License which applies to it and "any
later version", you have the option of following the terms and conditions
either of that version or of any later version published by the Free
Software Foundation. If the Program does not specify a version number of
this License, you may choose any version ever published by the Free Software
Foundation.
10. If you wish to incorporate parts of the Program into other free programs
whose distribution conditions are different, write to the author to ask for
permission. For software which is copyrighted by the Free Software
Foundation, write to the Free Software Foundation; we sometimes make
exceptions for this. Our decision will be guided by the two goals of
preserving the free status of all derivatives of our free software and of
promoting the sharing and reuse of software generally.
NO WARRANTY
11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR
THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN
OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES
PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED
OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO
THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM
PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR
CORRECTION.
12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR
REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES,
INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING
OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO
LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR
THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER
PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES.
END OF TERMS AND CONDITIONS
How to Apply These Terms to Your New Programs
If you develop a new program, and you want it to be of the greatest possible
use to the public, the best way to achieve this is to make it free software
which everyone can redistribute and change under these terms.
To do so, attach the following notices to the program. It is safest to
attach them to the start of each source file to most effectively convey the
exclusion of warranty; and each file should have at least the "copyright"
line and a pointer to where the full notice is found.
one line to give the program's name and an idea of what it does.
Copyright (C) yyyy name of author
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
Also add information on how to contact you by electronic and paper mail.
If the program is interactive, make it output a short notice like this when
it starts in an interactive mode:
Gnomovision version 69, Copyright (C) yyyy name of author
Gnomovision comes with ABSOLUTELY NO WARRANTY; for details
type `show w'. This is free software, and you are welcome
to redistribute it under certain conditions; type `show c'
for details.
The hypothetical commands `show w' and `show c' should show the appropriate
parts of the General Public License. Of course, the commands you use may be
called something other than `show w' and `show c'; they could even be
mouse-clicks or menu items--whatever suits your program.
You should also get your employer (if you work as a programmer) or your
school, if any, to sign a "copyright disclaimer" for the program, if
necessary. Here is a sample; alter the names:
Yoyodyne, Inc., hereby disclaims all copyright
interest in the program `Gnomovision'
(which makes passes at compilers) written
by James Hacker.
signature of Ty Coon, 1 April 1989
Ty Coon, President of Vice
This General Public License does not permit incorporating your program into
proprietary programs. If your program is a subroutine library, you may
consider it more useful to permit linking proprietary applications with the
library. If this is what you want to do, use the GNU Library General Public
License instead of this License.

GNU Free Documentation License

GNU Free Documentation License
Version 1.1, March 2000
Copyright (C) 2000 Free Software Foundation, Inc.
59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
0. PREAMBLE
The purpose of this License is to make a manual, textbook, or other written
document "free" in the sense of freedom: to assure everyone the effective
freedom to copy and redistribute it, with or without modifying it, either
commercially or noncommercially. Secondarily, this License preserves for the
author and publisher a way to get credit for their work, while not being
considered responsible for modifications made by others.
This License is a kind of "copyleft", which means that derivative works of
the document must themselves be free in the same sense. It complements the
GNU General Public License, which is a copyleft license designed for free
software.
We have designed this License in order to use it for manuals for free
software, because free software needs free documentation: a free program
should come with manuals providing the same freedoms that the software does.
But this License is not limited to software manuals; it can be used for any
textual work, regardless of subject matter or whether it is published as a
printed book. We recommend this License principally for works whose purpose
is instruction or reference.
1. APPLICABILITY AND DEFINITIONS
This License applies to any manual or other work that contains a notice
placed by the copyright holder saying it can be distributed under the terms
of this License. The "Document", below, refers to any such manual or work.
Any member of the public is a licensee, and is addressed as "you".
A "Modified Version" of the Document means any work containing the Document
or a portion of it, either copied verbatim, or with modifications and/or
translated into another language.
A "Secondary Section" is a named appendix or a front-matter section of the
Document that deals exclusively with the relationship of the publishers or
authors of the Document to the Document's overall subject (or to related
matters) and contains nothing that could fall directly within that overall
subject. (For example, if the Document is in part a textbook of mathematics,
a Secondary Section may not explain any mathematics.) The relationship could
be a matter of historical connection with the subject or with related
matters, or of legal, commercial, philosophical, ethical or political
position regarding them.
The "Invariant Sections" are certain Secondary Sections whose titles are
designated, as being those of Invariant Sections, in the notice that says
that the Document is released under this License.
The "Cover Texts" are certain short passages of text that are listed, as
Front-Cover Texts or Back-Cover Texts, in the notice that says that the
Document is released under this License.
A "Transparent" copy of the Document means a machine-readable copy,
represented in a format whose specification is available to the general
public, whose contents can be viewed and edited directly and
straightforwardly with generic text editors or (for images composed of
pixels) generic paint programs or (for drawings) some widely available
drawing editor, and that is suitable for input to text formatters or for
automatic translation to a variety of formats suitable for input to text
formatters. A copy made in an otherwise Transparent file format whose markup
has been designed to thwart or discourage subsequent modification by readers
is not Transparent. A copy that is not "Transparent" is called "Opaque".
Examples of suitable formats for Transparent copies include plain ASCII
without markup, Texinfo input format, LaTeX input format, SGML or XML using
a publicly available DTD, and standard-conforming simple HTML designed for
human modification. Opaque formats include PostScript, PDF, proprietary
formats that can be read and edited only by proprietary word processors,
SGML or XML for which the DTD and/or processing tools are not generally
available, and the machine-generated HTML produced by some word processors
for output purposes only.
The "Title Page" means, for a printed book, the title page itself, plus such
following pages as are needed to hold, legibly, the material this License
requires to appear in the title page. For works in formats which do not have
any title page as such, "Title Page" means the text near the most prominent
appearance of the work's title, preceding the beginning of the body of the
text.
2. VERBATIM COPYING
You may copy and distribute the Document in any medium, either commercially
or noncommercially, provided that this License, the copyright notices, and
the license notice saying this License applies to the Document are
reproduced in all copies, and that you add no other conditions whatsoever to
those of this License. You may not use technical measures to obstruct or
control the reading or further copying of the copies you make or distribute.
However, you may accept compensation in exchange for copies. If you
distribute a large enough number of copies you must also follow the
conditions in section 3.
You may also lend copies, under the same conditions stated above, and you
may publicly display copies.
3. COPYING IN QUANTITY
If you publish printed copies of the Document numbering more than 100, and
the Document's license notice requires Cover Texts, you must enclose the
copies in covers that carry, clearly and legibly, all these Cover Texts:
Front-Cover Texts on the front cover, and Back-Cover Texts on the back
cover. Both covers must also clearly and legibly identify you as the
publisher of these copies. The front cover must present the full title with
all words of the title equally prominent and visible. You may add other
material on the covers in addition. Copying with changes limited to the
covers, as long as they preserve the title of the Document and satisfy these
conditions, can be treated as verbatim copying in other respects.
If the required texts for either cover are too voluminous to fit legibly,
you should put the first ones listed (as many as fit reasonably) on the
actual cover, and continue the rest onto adjacent pages.
If you publish or distribute Opaque copies of the Document numbering more
than 100, you must either include a machine-readable Transparent copy along
with each Opaque copy, or state in or with each Opaque copy a
publicly-accessible computer-network location containing a complete
Transparent copy of the Document, free of added material, which the general
network-using public has access to download anonymously at no charge using
public-standard network protocols. If you use the latter option, you must
take reasonably prudent steps, when you begin distribution of Opaque copies
in quantity, to ensure that this Transparent copy will remain thus
accessible at the stated location until at least one year after the last
time you distribute an Opaque copy (directly or through your agents or
retailers) of that edition to the public.
It is requested, but not required, that you contact the authors of the
Document well before redistributing any large number of copies, to give them
a chance to provide you with an updated version of the Document.
4. MODIFICATIONS
You may copy and distribute a Modified Version of the Document under the
conditions of sections 2 and 3 above, provided that you release the Modified
Version under precisely this License, with the Modified Version filling the
role of the Document, thus licensing distribution and modification of the
Modified Version to whoever possesses a copy of it. In addition, you must do
these things in the Modified Version:
* A. Use in the Title Page (and on the covers, if any) a title distinct
from that of the Document, and from those of previous versions (which
should, if there were any, be listed in the History section of the
Document). You may use the same title as a previous version if the
original publisher of that version gives permission.
* B. List on the Title Page, as authors, one or more persons or entities
responsible for authorship of the modifications in the Modified
Version, together with at least five of the principal authors of the
Document (all of its principal authors, if it has less than five).
* C. State on the Title page the name of the publisher of the Modified
Version, as the publisher.
* D. Preserve all the copyright notices of the Document.
* E. Add an appropriate copyright notice for your modifications adjacent
to the other copyright notices.
* F. Include, immediately after the copyright notices, a license notice
giving the public permission to use the Modified Version under the
terms of this License, in the form shown in the Addendum below.
* G. Preserve in that license notice the full lists of Invariant Sections
and required Cover Texts given in the Document's license notice.
* H. Include an unaltered copy of this License.
* I. Preserve the section entitled "History", and its title, and add to
it an item stating at least the title, year, new authors, and publisher
of the Modified Version as given on the Title Page. If there is no
section entitled "History" in the Document, create one stating the
title, year, authors, and publisher of the Document as given on its
Title Page, then add an item describing the Modified Version as stated
in the previous sentence.
* J. Preserve the network location, if any, given in the Document for
public access to a Transparent copy of the Document, and likewise the
network locations given in the Document for previous versions it was
based on. These may be placed in the "History" section. You may omit a
network location for a work that was published at least four years
before the Document itself, or if the original publisher of the version
it refers to gives permission.
* K. In any section entitled "Acknowledgements" or "Dedications",
preserve the section's title, and preserve in the section all the
substance and tone of each of the contributor acknowledgements and/or
dedications given therein.
* L. Preserve all the Invariant Sections of the Document, unaltered in
their text and in their titles. Section numbers or the equivalent are
not considered part of the section titles.
* M. Delete any section entitled "Endorsements". Such a section may not
be included in the Modified Version.
* N. Do not retitle any existing section as "Endorsements" or to conflict
in title with any Invariant Section.
If the Modified Version includes new front-matter sections or appendices
that qualify as Secondary Sections and contain no material copied from the
Document, you may at your option designate some or all of these sections as
invariant. To do this, add their titles to the list of Invariant Sections in
the Modified Version's license notice. These titles must be distinct from
any other section titles.
You may add a section entitled "Endorsements", provided it contains nothing
but endorsements of your Modified Version by various parties--for example,
statements of peer review or that the text has been approved by an
organization as the authoritative definition of a standard.
You may add a passage of up to five words as a Front-Cover Text, and a
passage of up to 25 words as a Back-Cover Text, to the end of the list of
Cover Texts in the Modified Version. Only one passage of Front-Cover Text
and one of Back-Cover Text may be added by (or through arrangements made by)
any one entity. If the Document already includes a cover text for the same
cover, previously added by you or by arrangement made by the same entity you
are acting on behalf of, you may not add another; but you may replace the
old one, on explicit permission from the previous publisher that added the
old one.
The author(s) and publisher(s) of the Document do not by this License give
permission to use their names for publicity for or to assert or imply
endorsement of any Modified Version.
5. COMBINING DOCUMENTS
You may combine the Document with other documents released under this
License, under the terms defined in section 4 above for modified versions,
provided that you include in the combination all of the Invariant Sections
of all of the original documents, unmodified, and list them all as Invariant
Sections of your combined work in its license notice.
The combined work need only contain one copy of this License, and multiple
identical Invariant Sections may be replaced with a single copy. If there
are multiple Invariant Sections with the same name but different contents,
make the title of each such section unique by adding at the end of it, in
parentheses, the name of the original author or publisher of that section if
known, or else a unique number. Make the same adjustment to the section
titles in the list of Invariant Sections in the license notice of the
combined work.
In the combination, you must combine any sections entitled "History" in the
various original documents, forming one section entitled "History"; likewise
combine any sections entitled "Acknowledgements", and any sections entitled
"Dedications". You must delete all sections entitled "Endorsements."
6. COLLECTIONS OF DOCUMENTS
You may make a collection consisting of the Document and other documents
released under this License, and replace the individual copies of this
License in the various documents with a single copy that is included in the
collection, provided that you follow the rules of this License for verbatim
copying of each of the documents in all other respects.
You may extract a single document from such a collection, and distribute it
individually under this License, provided you insert a copy of this License
into the extracted document, and follow this License in all other respects
regarding verbatim copying of that document.
7. AGGREGATION WITH INDEPENDENT WORKS
A compilation of the Document or its derivatives with other separate and
independent documents or works, in or on a volume of a storage or
distribution medium, does not as a whole count as a Modified Version of the
Document, provided no compilation copyright is claimed for the compilation.
Such a compilation is called an "aggregate", and this License does not apply
to the other self-contained works thus compiled with the Document, on
account of their being thus compiled, if they are not themselves derivative
works of the Document. If the Cover Text requirement of section 3 is
applicable to these copies of the Document, then if the Document is less
than one quarter of the entire aggregate, the Document's Cover Texts may be
placed on covers that surround only the Document within the aggregate.
Otherwise they must appear on covers around the whole aggregate.
8. TRANSLATION
Translation is considered a kind of modification, so you may distribute
translations of the Document under the terms of section 4. Replacing
Invariant Sections with translations requires special permission from their
copyright holders, but you may include translations of some or all Invariant
Sections in addition to the original versions of these Invariant Sections.
You may include a translation of this License provided that you also include
the original English version of this License. In case of a disagreement
between the translation and the original English version of this License,
the original English version will prevail.
9. TERMINATION
You may not copy, modify, sublicense, or distribute the Document except as
expressly provided for under this License. Any other attempt to copy,
modify, sublicense or distribute the Document is void, and will
automatically terminate your rights under this License. However, parties who
have received copies, or rights, from you under this License will not have
their licenses terminated so long as such parties remain in full compliance.
10. FUTURE REVISIONS OF THIS LICENSE
The Free Software Foundation may publish new, revised versions of the GNU
Free Documentation License from time to time. Such new versions will be
similar in spirit to the present version, but may differ in detail to
address new problems or concerns. See http://www.gnu.org/copyleft/.
Each version of the License is given a distinguishing version number. If the
Document specifies that a particular numbered version of this License "or
any later version" applies to it, you have the option of following the terms
and conditions either of that specified version or of any later version that
has been published (not as a draft) by the Free Software Foundation. If the
Document does not specify a version number of this License, you may choose
any version ever published (not as a draft) by the Free Software Foundation.
How to use this License for your documents
To use this License in a document you have written, include a copy of the
License in the document and put the following copyright and license notices
just after the title page:
Copyright (c) YEAR YOUR NAME.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.1
or any later version published by the Free Software Foundation;
with the Invariant Sections being LIST THEIR TITLES, with the
Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.
A copy of the license is included in the section entitled "GNU
Free Documentation License".
If you have no Invariant Sections, write "with no Invariant Sections"
instead of saying which ones are invariant. If you have no Front-Cover
Texts, write "no Front-Cover Texts" instead of "Front-Cover Texts being
LIST"; likewise for Back-Cover Texts.
If your document contains nontrivial examples of program code, we recommend
releasing these examples in parallel under your choice of free software
license, such as the GNU General Public License, to permit their use in free
software.